Honeycomb filter and method for producing honeycomb filter

ABSTRACT

There is provided a honeycomb filter wherein particles having an average particle diameter smaller than the average pore diameter of partition walls are deposited at least in open pores formed in the surface layer of the partition wall and in the pores of the partition wall in a surface layer portion of the partition walls on the exhaust gas inflow side, thereby forming a composite region. The average pore diameter of the partition walls is 5 to 40 μm, and the porosity of the partition wall is 35 to 75%. The particles to be deposited have an average particle diameter of 1 to 15 μm, and the height of the composite region is not more than 80 μm in the direction from the outermost contour line of the partition walls to the surface of the partition walls.

TECHNICAL FIELD

The present invention relates to a honeycomb filter used for trapping orcleaning up particulates contained in exhaust gas discharged from aninternal combustion engine such as a diesel engine or various combustionapparatuses and to a method for producing the honeycomb filter.

BACKGROUND ART

A large mount of particulate matter (hereinbelow referred to as“particulate matter”, “particulates”, or “PM”) anchored by soot(graphite) is contained in exhaust gas discharged from an internalcombustion engine such as a diesel engine or various combustionapparatuses (hereinbelow appropriately referred to as “internalcombustion engine and the like”). Since environmental pollution iscaused when the particulates are released without change into theatmosphere, it is general that a filter for trapping particulates ismounted in the exhaust gas passage from the internal combustion engineor the like.

An example of the filter used for such a purpose is a honeycomb filterhaving a honeycomb structure having a plurality of cells separated bypartition walls formed of porous ceramic having a large number of poresand functioning as exhaust gas passages with one side open end portionsand the other side open end portions of plural cells being alternatelyplugged with plugging portions. In such a honeycomb filter, when exhaustgas is sent into the exhaust gas inflow cells (cells not plugged on theexhaust gas inflow side), particulates in the exhaust gas are trappedwhen exhaust gas passes through the partition walls, and purified gasfrom which the particulates are removed is discharged from the purifiedgas outflow cells (cells not plugged on the exhaust gas outflow side).

However, in such a conventional honeycomb filter, there arises a problemof easily causing pressure loss in the partition walls in accordancewith a deposition mode of soot or ash. In particular, in order to reducepressure loss to improve the trapping efficiency, it is effective toimpart properties of pores having a small average pore diameter to ahoneycomb filter. However, when a layer having such properties is formedon the partition walls of the honeycomb filter, pressure loss of thepartition walls is increased when the exhaust gas passes through thepartition walls at high flow rates. Therefore, in a conventionalhoneycomb filter, it is difficult to realize improvement in purificationperformance and regeneration efficiency simultaneously with planning thereduction of pressure loss.

For the aforementioned problems, there are the following PatentDocuments 1 and 2.

The Patent Document 1 discloses a ceramic filter “provided with a fineparticle portion having an average pore diameter of 1 to 10 μm and athickness of at least 10 times the average pore diameter on a surface onone side of a support layer formed of a ceramic filter porous body” forthe purpose of providing “a ceramic filter for exhaust gas, the filterhaving little change of pressure loss with the passage of time aftertrapping and high trapping efficiency and being excellent on practicalside.

The Patent Document 2 discloses a “surface filter for fine particles,the filter having passages selectively clogged and a micro porousmembrane imparted to the surfaces of the passages, being formed of aporous honeycomb monolith structure, and being regenerable by reverseflushing” for the purpose of providing “a new filtering apparatusregenerable by a reverse flushing treatment”.

However, the Patent Documents 1 and 2 aim to improve PM-trappingperformance by forming a layer having an average pore diameter smallerthan that of the partition walls on the partition walls. In such a case,the opening of the cell on the exhaust gas inflow side as an inletchannel becomes small for the thickness of the layer formed therein.Therefore, there arises a problem of remarkable increase in the pressureloss of the partition walls particularly when the exhaust gas passesthrough the partition walls at high flow rates. On the other hand,reduction of the thickness of the partition wall can be considered foravoiding the problem. However, since thermal capacity is reduced whenthe thickness of the partition walls is reduced, and inlet temperature(temperature of the exhaust gas inflow side end face in the honeycombfilter) may be varied upon regeneration to become higher than the targettemperature. In such a case, since quick combustion of soot may becaused to sharply raise the temperature inside the honeycomb filter, acrack may easily be caused in the honeycomb filter.

As described above, a response to the conventional problems is stillinsufficient even by the Patent Documents 1 and 2, and a solution in theearly stages is desired.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP-A-63-240912-   Patent Document 2: Japanese Utility Model Registration No. 2607898.

SUMMARY OF THE INVENTION

The present invention has been made in view of the aforementioned priorart problems and aims to provide a honeycomb filter capable of reducingpressure loss of the partition walls when exhaust gas passes through thepartition walls at high flow rates with obtaining the same effect as inthe layer formed on the partition walls by forming, at least in poresformed in the surface layer of the partition walls and pores in thepartition walls, a composite region by depositing particles having anaverage particle diameter smaller than the average pore diameter of theaforementioned partition walls in a surface layer portion of thepartition walls on the exhaust gas inflow side, allowing the partitionwalls to have an average pore diameter of 5 to 40 μm and a porosity of35 to 75%, allowing the particles deposited to have an average particlediameter of 1 to 15 μm, and allowing the composite region to have aheight of 80 μm or less with respect to the partition wall surfacedirection from the outermost contour line of the partition walls; and amethod for producing the honeycomb filter. In addition, the presentinvention aims to provide a honeycomb filter improving regenerationefficiency with improving purification performance, a honeycomb filterimproving high trapping efficiency with reducing pressure loss due tothe adhesion of soot, and a honeycomb filter reducing the pressure lossafter ash deposition; and a method for producing the honeycomb filter.

According to the present invention, there are provided the followinghoneycomb filter and method for producing the honeycomb filter.

[1] A honeycomb filter comprising a base material having a honeycombstructure provided with a plurality of cells separated by partitionwalls of porous ceramic having pores and functioning as exhaust gaspassages, wherein plugging portions are formed alternately in one sideopen end portions and the other side open end portions of the pluralcells, at least in pores formed in a surface layer of the partitionwalls and pores in the partition walls, a composite region is formed bydepositing particles having an average particle diameter smaller than anaverage pore diameter of the partition walls in a surface layer portionof the partition walls on the exhaust gas inflow side, the partitionwalls have an average pore diameter of 5 to 40 μm and a porosity of 35to 75%, the particles deposited have an average particle diameter of 1to 15 μm, and the composite region has a height of 80 μm or less withrespect to the partition wall surface direction from the outermostcontour line of the partition walls.

[2] The honeycomb filter according to [1], wherein the composite regionis formed in the pores formed in the surface layer of the partitionwalls and the pores in the partition walls in the range from a surfacelayer reference line of the partition walls on the exhaust gas inflowside to a position of 30% of the partition wall thickness.

[3] The honeycomb filter according to [1] or [2], wherein the compositeregion is formed in the pores formed in the surface layer of thepartition walls and the pores in the partition walls in the range from asurface layer reference line of the partition wall on the exhaust gasinflow side to a position of the depth of at most 4 times the averagepore diameter of the partition walls.

[4] The honeycomb filter according to any one of [1] to [3], wherein thepartition walls have a porous structure constituted of a pore-linkedform and wherein the composite region has a porous structure constitutedof a particle-liked form.

[5] The honeycomb filter according to any one of [1] to [4], wherein theparticles to be deposited in the pores formed in the surface layer ofthe partition walls and the pores in the partition walls are formed ofthe same material as that for the partition walls.

[6] The honeycomb filter according to any one of [1] to [5], wherein thepartition walls are of cordierite or aluminum titanate.

[7] The honeycomb filter according to any one of [1] to [6], wherein theparticles to be deposited in the pores formed in the surface layer ofthe partition walls and the pores in the partition walls are connectedto one another by sintering of the particles.

[8] The honeycomb filter according to any one of [1] to [7], wherein acatalyst is loaded on a part of or the entire portion of the partitionwalls and/or a part of or the entire portion of the composite region.

[9] A method for producing a honeycomb filter, the method comprising:forming a honeycomb formed article by subjecting a forming raw materialcontaining a ceramic raw material to extrusion forming and formingplugging portions alternately in one side open end portions and theother side open end portions of the other cells of the honeycomb formedbody, firing the honeycomb formed body to form a honeycomb fired body,supplying particles having an average particle diameter smaller than theaverage pore diameter of the partition walls from the one side open endportions of the honeycomb fired body by a solid-gas two-phase flow, andat least in pores formed in the surface layer of the partition walls andthe pores in the partition walls, forming a composite region bydepositing particles having an average particle diameter smaller thanthe average pore diameter of the partition walls in a surface layerportion of the partition walls on the exhaust gas inflow side; whereinthe partition walls have an average pore diameter of 5 to 40 μm and aporosity of 35 to 75%, the particles deposited have an average particlediameter of 1 to 15 μm, and the composite region has a height of 80 μmor less with respect to the partition wall surface direction from theoutermost contour line of the partition walls.

[10] A method for producing a honeycomb filter, the method comprising:forming a honeycomb formed body by subjecting a forming raw materialcontaining a ceramic raw material to extrusion forming and formingplugging portions alternately in one side open end portions and theother side open end portions of the other cells of the honeycomb formedbody, firing the honeycomb formed article to form a honeycomb firedarticle, supplying particles having an average particle diameter smallerthan the average pore diameter of the partition walls from the one sideopen end portions of the honeycomb fired article by a solid-gastwo-phase flow, at least in pores formed in the surface layer of thepartition walls and pores in the partition walls, forming a compositeregion by depositing particles having an average particle diametersmaller than the average pore diameter of the partition walls in asurface layer portion of the partition walls on the exhaust gas inflowside, and further performing a thermal treatment; wherein the partitionwalls have an average pore diameter of 5 to 40 μm and a porosity of 35to 75%, the particles deposited have an average particle diameter of 1to 15 μm, and the composite region has a height of 80 μm or less withrespect to the partition wall surface direction from the outermostcontour line of the partition walls.

[11] A method for producing a honeycomb filter, the method comprising:forming a honeycomb formed body by subjecting a forming raw materialcontaining a ceramic raw material to extrusion forming and formingplugging portions alternately in one side open end portions and theother side open end portions of the other cells of the honeycomb formedbody, firing the honeycomb formed body to form a honeycomb fired body,loading a catalyst on the partition walls of the honeycomb fired body toobtain a catalyst-loaded honeycomb-structured body, supplying particleshaving an average particle diameter smaller than the average porediameter of the partition walls from the one side open end portions ofthe catalyst-loaded honeycomb-structured body by a solid-gas two-phaseflow, at least in pores formed in the surface layer of the partitionwalls and pores in the partition walls, forming a composite region bydepositing particles having an average particle diameter smaller thanthe average pore diameter of the partition walls in a surface layerportion of the partition walls on the exhaust gas inflow side, andfurther performing a thermal treatment; wherein the partition walls havean average pore diameter of 5 to 40 μm and a porosity of 35 to 75%, theparticles deposited have an average particle diameter of 1 to 15 μm, andthe composite region has a height of 80 μm or less with respect to thepartition wall surface direction from the outermost contour line of thepartition walls.

[12] The method for producing a honeycomb filter according to any one of[9] to [11], wherein the method comprises: supplying particles having anaverage particle diameter smaller than the average pore diameter of thepartition walls from one side open end portion of the honeycomb firedbody, and simultaneously, sucking the particles from the other open endportions of the honeycomb fired body to deposit the particles in thepores formed in the partition walls on the exhaust gas inflow side toform a composite region.

According to a filter of the present invention, there is exhibited anexcellent effect of being capable of providing a honeycomb filtercapable of reducing pressure loss of the partition walls when exhaustgas passes through the partition walls at high flow rates with obtainingthe same effect as in the layer formed on the partition walls byforming, at least in pores formed in a surface layer of the partitionwalls and pores in the partition walls, a composite region by depositingparticles having an average particle diameter smaller than the averagepore diameter of the aforementioned partition walls in a surface layerportion of the partition walls on the exhaust gas inflow side, allowingthe partition walls to have an average pore diameter of 5 to 40 am and aporosity of 35 to 75%, allowing the particles deposited to have anaverage particle diameter of 1 to 15 μm, and allowing the compositeregion to have a height of 80 μm or less with respect to the partitionwall surface direction from the outermost contour line of the partitionwalls; and a method for producing the honeycomb filter. In addition,there are provided a honeycomb filter improving regeneration efficiencywith improving purification performance, a honeycomb filter improvinghigh trapping efficiency with reducing pressure loss due to the adhesionof soot, and a honeycomb filter reducing the pressure loss after ashdeposition; and a method for producing a honeycomb filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a honeycomb filter to which anembodiment of the present invention is applied and plan view of thehoneycomb filter.

FIG. 2 is a schematic view showing the honeycomb filter of FIG. 1 andperspective view of the honeycomb filter.

FIG. 3 is a cross-sectional view of the honeycomb filter of FIG. 1 andview shown schematically.

FIG. 4A is a partial cross-sectional view schematically showing a partof a partition wall of the honeycomb filter in the present embodiment.

FIG. 4B is a partial cross-sectional view schematically showing a partof a partition wall of the honeycomb filter in the present embodiment.

FIG. 5A is a partial cross-sectional view schematically showing a partof a partition wall of a conventional honeycomb filter.

FIG. 5B is a partial cross-sectional view schematically showing a partof a partition wall of a conventional honeycomb filter.

FIG. 5C is a partial cross-sectional view schematically showing a partof a partition wall of a conventional honeycomb filter.

FIG. 5D is a graph showing the relation between the soot depositionamount and the pressure loss of the partition wall.

FIG. 5E is a partial cross-sectional view schematically showing a partof a partition wall of a conventional honeycomb filter.

FIG. 6 is a graph showing the relation between the ash deposition amountand the pressure loss of the partition wall by soot.

FIG. 7 is a graph showing the relation between the soot depositionamount in each step in engine drive and the pressure loss of thepartition wall by soot.

FIG. 8A is a partial cross-sectional view of a partition wall of aconventional honeycomb filter and view schematically showing a sootdeposition condition of a partition wall in the initial stage in enginedrive.

FIG. 8B is a partial cross-sectional view of a part of a cell of aconventional honeycomb filter, schematically showing the soot depositioncondition in FIG. 8A in the cell longitudinal direction.

FIG. 9A is a partial cross-sectional view of a partition wall of aconventional honeycomb filter, schematically showing a soot depositionstate of the partition wall in the initial stage in engine drive.

FIG. 9B is a view schematically showing the soot deposition state inFIG. 9A in the cell longitudinal direction.

FIG. 10A is a partial cross-sectional view of a partition wall of aconventional honeycomb filter, schematically showing a soot depositionstate of the partition wall after repeated regeneration.

FIG. 10B is a view schematically showing the soot deposition state ofFIG. 10A in the cell longitudinal direction.

FIG. 11 is a partial cross-sectional view of a partition wall of thehoneycomb filter of the present embodiment, schematically showing theoutermost contour line.

FIG. 12 is a partial cross-sectional view of a partition wall of thehoneycomb filter of the present embodiment, schematically showing theoutermost contour line.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, a mode for carrying out a honeycomb filter of the presentinvention are specifically described. However, the present inventionwidely includes honeycomb filters provided with the subject matter ofthe present invention and is not limited to the following mode.

[1] Honeycomb Filter of the Present Invention:

As shown in FIGS. 1 to 4A, the honeycomb filter 1 of the presentinvention is constituted as a honeycomb filter 1 having ahoneycomb-structured substrate provided with a plurality of cells 3separated by partition walls 4 of porous ceramic having pores, whereinplugging portions 13 are formed alternately in one side open endportions 11 a and the other side open end portions 11 b of the pluralcells 3, at least in pores 7 formed in the surface layer of thepartition walls 4 and pores in the partition walls, a composite regionis formed by depositing particles 5 having an average particle diametersmaller than the average pore diameter of the partition walls 4 in asurface layer portion 4 a of the partition walls on the exhaust gasinflow side, the partition walls 4 have an average pore diameter of 5 to40 μm and a porosity of 35 to 75%, the particles deposited have anaverage particle diameter of 1 to 15 μm, and the composite region has aheight of 80 μm or less with respect to the partition wall surfacedirection from the outermost contour line of the partition walls.

[1-1] Composite Region:

The composite region in the present embodiment is formed by depositingparticles having an average particle diameter smaller than the averagepore diameter of the aforementioned partition walls at least in openpores formed in the surface layer of the partition walls and the poresin the partition walls. That is, the composite region is constituted asa composite layer composed of the surface layer of the partition walland the particles deposited therein by depositing particles having anaverage particle diameter smaller than the average pore diameter of thepartition walls at least in pores formed in the surface layer of thepartition walls and pores in the partition walls in a surface layerportion of the partition walls on the exhaust gas inflow side. Thereason why the composite region is formed in the surface layer portionof the partition walls on the exhaust gas inflow side is because thepressure loss incidence rate is reduced to improve the PM trappingefficiency even without imparting properties of pores having smallaverage pore diameter to the partition walls. In other words, evenwithout forming a layer having properties of pores having a smallaverage pore diameter on the partition walls, by forming the compositeregion of the present embodiment, the pressure loss incidence rate ofpartition walls caused when the exhaust gas passes through the partitionwalls at high flow rates can be reduced with obtaining the same effectas in the formation of a layer having properties of pores having a smallaverage pore diameter on the partition walls.

That is, by forming the composite region by depositing particles havingan average particle diameter smaller than the average pore diameter ofthe partition walls in pores formed in the surface layer of thepartition walls and pores in the partition walls, the particles asso-called “simulated ash” are deposited in the pores formed in thesurface layer of the partition walls and pores in the partition walls.The particles (particles having an average particle diameter smallerthan the average pore diameter of the partition walls) as the “simulatedash” inhibit soot and ash from entering the pores formed in the surfacelayer of the partition walls and pores in the partition walls.Therefore, the deposition of soot and ash can be controlled, andreduction of the pressure loss incidence rate in the partition walls canbe realized.

Further, in the composite region, the particles having an averageparticle diameter smaller than the average pore diameter of thepartition walls may be connected to one another in the pores and poresin the partition walls in the surface layer portion of the partitionwalls on the exhaust gas inflow side. The thus connected particlesdeposit in, for example, pores on the downstream side with respect tothe surface layer portion of the partition walls and pores in thepartition walls and/or the region on the upstream side with respect tothe surface layer portion of the partition walls. The particlesconnected to one another are present so as to cover a part of or theentire range of the pores formed in the surface layer of the partitionwalls and the pores in the partition walls. The particles connected toone another also form the particle assemblage or particle layerdescribed later.

For example, as shown in FIG. 5A, there is a conventional honeycombfilter (hereinbelow appropriately referred to as a “conventionalhoneycomb filter”) composed of a two-layer structure having a layerhaving an average pore diameter smaller than that of the partition wall114 and formed on the partition walls 114 as an inlet layer 115 and thepartition wall. In comparison with the conventional honeycomb filter,the difference of the present embodiment is clear. Incidentally, in FIG.5A, for convenience of explanation, a line is drawn at the boundary ofthe inlet layer 115 and the partition wall 114. In addition, the same isapplied to FIGS. 5B, 5C, and 5E described later.

In the partition walls with which the conventional honeycomb filter isprovided, specifically, there were a case (1) of generating pressureloss in the partition walls due to deposition of soot in the partitionwalls and a case (2) of generating pressure loss in the partition wallsdue to deposition of ash in the partition walls. Further, there was acase (3) of generating pressure loss by having both (1) and (2)together.

An example of the case (1) of generating pressure loss in the partitionwall due to deposition of soot in the partition walls is as follows. Inthe first place, soot enters in the pores which are partition walls onthe exhaust gas inlet side and formed in the surface layer portion ofthe partition walls and in the pores in the partition walls. The soothaving entered in the pores deposits in the pores formed in the surfacelayer in the partition walls and in the pores in the partition walls tohave a saturated state in the pores formed in the surface layer portionand in the pores in the partition walls. Further, after the saturationin the pores, soot deposits on the partition walls to form a so-calledcake layer. Thus, the pressure loss of the partition walls of (1) couldbe caused in the deposition mode where soot deposits.

Description will be given specifically with referring to drawings. Asshown in FIG. 5B, in the initial stage where the engine is continuouslydriven a shot time, since the soot 117 does not sufficiently deposit onor in the partition walls, the soot enters the pores formed in thesurface layer of the partition walls of the inlet layer 115 and thepores in the partition walls. That is, as shown in FIG. 5B, the pressureloss of the partition walls attributed to the soot is caused by thestress applied to the partition walls when the soot 117 enters the poresformed in the surface layer of the partition walls and the pores in thepartition walls to do damage to the partition walls. In other words, asshown in FIG. 5C, in the case that the soot 117 deposits sufficiently inthe pores formed in the surface layer of the partition walls and thepores in the partition walls to have a saturated state or that the sootdeposits sufficiently on the partition walls to form a cake layer, soothardly enters or cannot enter the pores formed in the surface layer ofthe partition walls and the pores in the partition walls. Therefore,pressure loss of the partition walls by the soot is hardly caused. Thisis clear also from FIGS. 5D and 5E showing the relation between the sootdeposition amount and the pressure loss. In the initial stage of enginedrive, as shown in FIG. 5D, the amount of soot entering the pores formedin the surface layer of the partition walls and the pores in thepartition walls is high, and soot enters in the region of I shown inFIG. 5E to raise the possibility of causing pressure loss in thepartition walls. However, when the pores formed in the surface layer ofthe partition walls and the pores in the partition walls have asaturated state after the soot enters in the pores formed in the surfacelayer of the partition walls and the pores in the partition walls, orwhen a cake layer is formed after the soot deposits on the partitionwalls, as shown in FIG. 5E, the state where the soot deposits in theregion of II is shown. Therefore, as shown in FIG. 5D, the amount ofsoot entering the pores formed in the surface layer of the partitionwalls and the pores in the partition walls is reduced, thereby reducingthe pressure loss incidence rate of the partition walls due to entry ofthe soot. Thus, there is a high possibility of causing the pressure lossof the partition walls by the soot in the initial stage where the engineis not continuously driven. On the other hand, in the stage where theengine is continuously driven, which is the stage next to the initialstage, there is a low possibility of causing the pressure loss of thepartition walls. Therefore, the problem was how to eliminate thepossibility of pressure loss of the partition walls which can repeatedlybe caused upon soot combustion in the regeneration control, with tryingto reduce pressure loss of the partition walls in the initial stage.

In addition, as an example of the case (2) of generating pressure lossin the partition wall due to deposition of ash in the partition walls,it could happen when ash enters the pores which are partition walls onthe exhaust gas inlet side and formed in the surface layer portion ofthe partition walls and the pores in the partition walls, or ash damagesthe surfaces of the partition walls in the state that the sootdeposition on the partition walls is insufficient. Specifically, asshown in FIG. 5A, in the initial stage where the engine is not drivencontinuously, soot is not deposited on the partition walls or in thepores formed in the surface layer of the partition walls and the poresin the partition walls. That is, there is no so-called shielding layerwhich inhibits ash from entering the pores formed in the surface layerof the partition walls and the pores in the partition walls. Therefore,ash has various shapes and sizes and easily enters the pores formed inthe surface layer of the partition walls and the pores in the partitionwalls in the state that no soot is deposited.

Further, ash is discharged from the engine with being mixed in the sootand flows into the passages (cells) of the honeycomb filter. Therefore,the deposition modes of soot and ash are simultaneously performed (3).The deposition modes of soot and ash have two prominent stages (Phase Aand Phase B), and the pressure loss of the partition walls is causedfrom the composite factor.

In the first stage (Phase A, hereinbelow appropriately referred to asthe “first stage” or “phase A”), there is shown a general behaviorshowing that the pressure loss of the partition walls (ash depositionpressure loss behavior) is caused by the deposition of ash. In this ashdeposition pressure loss behavior is clear from the relation between thepressure loss of the partition walls attributing to the soot and theamount of ash shown in FIG. 6. That is, in the engine drive initialstage, since no soot is deposited in the surface layer portion of thepartition walls on the exhaust gas inflow side, there is a highpossibility of generating pressure loss of the partition walls becausesoot and ash are mixed and enter the pores formed in the surface layerof the partition walls and the pores in the partition walls to bedeposited (see point a of FIG. 6).

Next, in the termination of the first stage (Phase A), soot is combustedby repeatedly regenerating a honeycomb filter. However, since ash is notcombusted, ash gradually deposits in the pores formed in the surfacelayer of the partition walls and the pores in the partition walls. Thus,in the termination of the first stage (Phase A), ash deposited in thepores formed in the surface layer of the partition walls and the poresin the partition walls by the repeated regeneration of the honeycombfilter inhibits soot from entering the pores formed in the surface layerof the partition walls and the pores in the partition walls. As aresult, the pressure loss of the partition walls is reduced (see point bof FIG. 6).

Further, when the regeneration of the honeycomb filter is repeated, ashcontained in the soot is sent toward the downstream side of the cells(inlet cells) open at the inlet of the exhaust gas upon regeneration.Then, ash deposits on the plugging portions on the exhaust gas outletside. Therefore, the effective volume of the inlet cells is graduallyreduced. As a result, the thickness of the soot layer when a certainamount of soot deposits becomes large, and the partition wall permeationflow rate (flow rate when exhaust gas permeates the partition walls)becomes high, thereby raising the pressure loss of the honeycomb filter(DPF). This corresponds to the second stage (Phase B, hereinbelowappropriately referred to as the “second stage” or “phase B”) (see PhaseB of FIG. 6). Incidentally, “cell effective volume” means the capacityof the space where exhaust gas can pass and/or the space in the inletcells where the soot can deposit. The smaller cell effective volume hasa higher tendency of rise in exhaust gas permeation flow rate and ahigher tendency of increase in thickness of the soot layer formed on thepartition walls upon soot deposition. Therefore, the pressure lossincidence rate of the partition walls in the honeycomb filter (DPF)rises. Here, the exhaust gas permeation flow rate means the speed whenexhaust gas permeates the partition walls, that is, the speed when theexhaust gas passes through the pores of the partition walls.

In such two stages (Phase A and Phase B), the pressure loss incidencerate of the partition walls is hardly reduced, or the regenerationefficiency is hardly improved. For example, as shown in FIG. 7 showingthe relation between the soot deposition amount and the pressure loss ofthe partition walls by soot deposition, in the initial stage where noash is deposited of the graph a, as shown in FIGS. 8A and 8B, since noash deposits in the pores of the partition walls, the cell effectivevolume is sufficient. However, the pressure loss incidence rate of thepartition walls by soot cannot be reduced sufficiently, which is notpreferable. On the other hand, as shown in the graph c of FIG. 7, in astate where sufficient ash is deposited (state where the regenerationtreatment is performed repeatedly), the pressure loss of the partitionwalls by soot can be reduced. However, the cell effective volume is notsufficient, and soot is sent toward the downstream side as shown inFIGS. 10A and 10B, which is not preferable.

Therefore, the present embodiment employs not only the two-layerstructure where a layer of particles having an average pore diametersmaller than the average particle diameter of the particles constitutingthe partition walls is formed on the partition walls, but also theaforementioned structure. For example, the present embodiment employs astructure where the state of sufficient ash deposition of the graph b ofFIG. 7 is added in advance. By such constitution, the effect ofimprovement in the soot combustion and regeneration efficiency isrealized by securing the cell effective volume with reducing thepressure loss incidence rate of the partition walls as shown in FIGS. 9Aand 9B. Above all, the regeneration efficiency is improved with reducingthe pressure loss incidence rate of the partition walls regardless ofthe period of use of the engine.

In other words, in the present embodiment, as shown in FIG. 4A, byforming the composite region 4 a by depositing the particles 5 having anaverage particle diameter smaller than the average pore diameter of thepartition walls at least in the pores 7 formed in the surface layer ofthe partition walls 4 and the pores in the partition walls in a surfacelayer portion 4 a of the partition walls on the exhaust gas inflow side,soot and ash are inhibited from entering the pores 7 formed in thesurface layer of the partition walls and the pores in the partitionwalls as shown in FIG. 4B.

Here, the aforementioned “partition walls on the exhaust gas inflowside” means the partition walls formed on the exhaust gas inflow side inthe honeycomb-structured substrate. Specifically, as shown in FIGS. 3 to5, the partition walls on the exhaust gas inflow side correspond withthe inlet ports of the exhaust gas inflow passages in the partitionwalls 4 which the cells 3 have and the region in the vicinity of theinlet ports.

In addition, the “surface layer portion” of the partition walls on theexhaust gas inflow side means the region on the exhaust gas inflow sidein the region in the partition wall thickness direction and the regionin the vicinity of the region. Specifically, as the region 4 a shown inFIG. 4A, the region is the region on the exhaust gas inflow side in theregion in the partition wall thickness direction on the exhaust gasinflow side and the region in the vicinity of the region.

In addition, the “pores” formed in the surface layer of the partitionwalls mean the pores which the exhaust gas can enter without beingclosed among the pores formed in the partition walls. That is, the poresare “open pores” (hereinbelow, appropriately referred to as “openpores”) where the pore surfaces in the pores of the partition walls areexposed to the partition wall and where a part of or the entire poresurface forms a part of the surface layer of the partition wall. Inother words, the “closed pores” which the exhaust gas cannot enter withbeing closed are excluded even if the pores are formed by theaforementioned partition walls. An example is an open pore which exhaustgas can flow in and flow out without being closed if particles do notdeposit as the pore shown by the reference numeral 7 in FIG. 4A.

In addition, the reason why the particles having an average particlediameter smaller than the average pore diameter of the partition wallsare deposited at least in the open pores formed in the surface layer ofthe partition walls and the pores in the partition walls in the surfacelayer portion of the partition walls on the exhaust gas inflow side isbecause, even if deposition of the particles having an average particlediameter larger than the average pore diameter of the partition walls istried, the particles hardly deposit in the open pores in the surfacelayer portion of the partition walls and the pores in the partitionwalls. Further, the open pores in the surface layer portion of thepartition walls and the pore in the partition walls cannot be cloggedsufficiently. As a result, it becomes hard to sufficiently trap soot inthe composite region. In addition, soot passes through the compositeregion to easily deposit in the open pores of the partition walls formedon the downstream side of the composite region and pores in thepartition walls. Therefore, soot deposition similar to the case of theconventional partition wall having two-layered structure is caused, andthere is a high possibility of causing pressure loss in the partitionwalls. Thus, the particles to be deposited hardly play a role as theaforementioned “simulated ash”.

On the other hand, when the average particle diameter of the particlesto be deposited is smaller than the average pore diameter of thepartition walls, adhesion to the aforementioned open pores and pores inthe partition walls becomes easy. However, when the average particlediameter of the particles to be deposited is too small, the particleshaving a small average particle diameter pass through the open poresformed in the surface layer of the partition walls and pores in thepartition walls. In addition, the particles may deposit inside thepartition walls other than the aforementioned open pores and pores inthe partition walls. Therefore, in the inside of the partition walls,the connection portion of the pores of the partition walls is locallyclogged, and the gas permeability at the time when exhaust gas permeatesthe partition walls is prone to be deteriorated. By the low gaspermeability, the pressure loss incidence rate in the partition walls israised to a great extent, which is not preferable. Therefore, it isdesirable to form the composite region by adjusting the particles to bedeposited to have an appropriate size (average particle diameter).

Here, “connection portion” of the pores of the partition walls means aportion where pores are connected to one another in a pore passage whereplural pores formed by pore former are connected to one another in thepartition walls formed of a raw material such as cordierite, aluminumtitanate, or the like, and where the inner diameter of the pore issmall. In other words, it means a portion where the diameter of theexhaust gas passage is the smallest.

Incidentally, since the size of soot is generally about 100 nm on anaverage, and the size of ash is about 1 μm on an average, it ispreferable that the particles to be deposited have an appropriate size(average particle diameter) which suits these sizes.

In addition, the “particles having an average particle diameter smallerthan the average pore diameter of the partition walls” means that theparticles to be deposited in the open pores and pores in the partitionwalls have an average particle diameter smaller than the average porediameter of the partition walls. The average pore diameter of thepartition walls is measured by mercury penetration method. In addition,the average particle diameter of the particles to be deposited can becalculated by the image analysis from the photograph of a polished faceor a fracture face of a SEM. Incidentally, the contribution to thereduction of pressure loss with soot (partition wall pressure losscaused by the deposition of soot in open pores and pores in thepartition walls) basically depends on the absolute value of the particlediameter of particles forming the composite region (particles to bedeposited) and the deposition state and deposition distribution of theparticles to be deposited in the composite region. Therefore, it is notdetermined only by the ratio of the average particle diameter of theparticles to be deposited to the average pore diameter of the partitionwalls. That is, even if the composite region is constituted by the useof particles having the same average particle diameter as that of theparticles to be deposited, in the case that the average pore diameter ofthe partition walls is very large, or in the case that the porosity ofthe partition walls is very high, the particles (deposited particles)having an average particle diameter smaller than the average porediameter of the partition walls do not stay in the composite region, andmany particles enter the pores of the partition walls to easily clogpores. Therefore, there may be caused a defect such as remarkable riseof the pressure loss incidence rate of the partition walls. Accordingly,it is preferable to deposit desired “particles having an averageparticle diameter smaller than that of the particles” according to theabsolute value of the diameter of the particles (deposited particles)forming the composite region, the deposition condition of the particlesdeposited in the composite region, and the deposition distribution.

[1-1-1] Particles to be Deposited (Simulated Ash):

The composite region of the present embodiment is formed by depositingparticles having an average particle diameter smaller than the averagepore diameter of the partition walls at least in the pores formed in thesurface layer of the partition walls and pores of the partition walls.That is, “particles to be deposited” constitute a part of the compositeregion and are deposited on the partition walls as “simulated ash” asdescribed above (hereinbelow, the “particles to be deposited” areappropriately referred to as “simulated ash”). By depositing particlesas simulated ash, soot and ash can be inhibited from entering the openpores and the pores in the partition walls in the composite region evenin the engine initial rotational state where the soot and ash do notdeposit on the partition walls or in the open pores of the partitionwalls and the pores in the partition walls. Therefore, pressure loss ofthe partition walls can be inhibited from being caused.

In addition, the soot inhibited from entering the open pores and thepores in the partition walls by the particles as the simulated ash iscombusted upon regeneration. Therefore, since soot does not deposit evenby the repeated regeneration, the effective area of the honeycomb filteris not reduced. Further, no influence is received from the engine drivetime or the deposition mode of soot and ash. In other words, regardlessof the engine start-up time or the continuous drive time, the pressureloss incidence rate of the partition wall can be reduced. In addition,since soot can be inhibited from entering the pores of the partitionwalls, ash contained in the soot, particularly, sulfur componentcontained in the ash can be inhibited from contacting the catalyst evenin the case that a catalyst is loaded in the pores of the partitionwalls. Therefore, the catalyst can be inhibited from deteriorating.

In addition, the average pore diameter of the particles deposited in thepores formed in the surface layer of the partition walls and the poresin the partition walls is 1 to 15 μm. The average pore diameter of theparticles deposited is preferably 1 to 5 μm. When it is smaller than 1μm, since the packing density in the open pores and the pores of thepartition walls becomes high to fill the pores, the pressure lossincidence rate of the partition walls is raised. When it is larger than15 μm, since the space region of the open pores and the pores of thepartition walls cannot be clogged efficiently, PM easily passes throughthe space region. Therefore, sufficient trapping efficiency cannot beobtained. Incidentally, the average pore diameter of the partition wallsis measured by mercury penetration method. In addition, the averageparticle diameter of the particles to be deposited can be measured by animage analysis of a photograph of the polished surface or a fractureface by a SEM.

The height of the composite region is 80 μm or less with respect to thepartition wall surface direction from the outermost contour line of thepartition walls. This enables the particles to easily stay in the openpores and the pores in the partition walls. In other words, thedeposited particle hardly flows toward the adjacent cell side (so tospeak, exhaust gas outlet side) on the downstream side of the compositeregion from the open pores and the pores in the partition walls when theexhaust gas flows into the partition walls and flows out from thepartition walls. Further, the hydraulic diameter of the cell inlet(unplugged cell serving as an inlet for exhaust gas) can be securedsufficiently. Above all, pressure loss of the partition walls in theregion (high flow rate region) where exhaust gas passes at high flowrates can be inhibited. On the other hand, when it is larger than 80 μm,the hydraulic diameter of the cell inlet becomes small to raise thepressure loss incidence rate of the partition walls particularly in thehigh flow rate region, which is not preferable. It is more preferably 30μm or less.

Incidentally, the aforementioned composite region may be constituted ofa particle assemblage where the particles to be deposited form anassemblage, or, a particle layer where particle assemblages areconnected to one another to form a layer. In the particle assemblages,for example, an assemblage of particles where the particles to bedeposited are formed of plural particles or an assemblage whereparticles are connected to one another is included. On the other hand,by a thermal treatment, that is, addition of pore former and the likeupon subjecting the material to reaction sintering, the pore structureformed is eliminated. In other words, it means the state where the porestructure formed by connecting the spaces (pores) formed by the poreformer is eliminated to allow the assemblages of particles to bedispersed (sprinkled) as an assemblage in the open pores and the poresin the partition walls. Examples of the formation of the particleassemblages are the formation by mixing silica or the like in ceramicparticles or the like and the formation by depositing only simpleceramic particles on the partition walls. However, the formation is notlimited to these.

In addition, the “outermost contour line of the partition wall” means asupposition line (virtual line) for separating a partition wall and acell and contour line located on the outermost side among the linesforming the contour line of the partition wall. That is, the “outermostcontour line of the partition wall” means the outermost contour line ofthe partition wall and supposition outermost contour line formed uponconnecting the points where the outer contour line is separated from theprojection line. Further, in open pores formed in a surface of thepartition walls, when the diameters of the open pores on the downstreamside are larger than those in the surface layer of the partition walls,the projection line separates from the pore surface, and the virtualline obtained by drawing a line parallel to the surface layer referenceline described later from the point corresponds to the “outermostcontour line”. Specifically, the contour line forming the outermostcontour of the partition walls is present in the region of the partitionwall which is the nearest to the boundary separating the passage (cell)where a fluid flows from the partition wall, and such a suppositionalcontour line obtained by connecting the particles serves as the“outermost contour line”. Further, though the partition wall appears tobe formed into an almost flat and smooth plate shape by eye observation,it can be confirmed that numerous irregularities are formed on thecontour of the partition walls. It is preferable to deposit theparticles, particle assemblages, and particle layer in the region fromthe supposition line obtained by connecting, parallel to the surfacelayer reference line, the points where the aforementioned particles inthe region along the concave or convex contour of the partition wallshaving numerous irregularities separate from the projection line in thepores to at least the surface of the partition wall.

In addition, the “surface layer reference line” shows the average heightof the irregularities of the surface layer in one visual field.

Therefore, “the composite region has a height of 80 μm or less withrespect to the partition wall surface direction from the outermostcontour line of the partition walls” means that, in the case that theparticles to be deposited in the open pores and the pores in thepartition walls form the aforementioned composite region, the particlesare present in the region (open pores and the pores in the partitionwalls) within 80 μm in the partition wall thickness direction (directionperpendicular to the partition wall) from the outermost contour line ofthe partition wall toward the partition wall surface. Incidentally, inthe case that the particles to be deposited in the open pores and thepores in the partition walls form the aforementioned composite region asparticle assemblages of assemblages, it means that the particleassemblages are present in the region (in the open pores and the poresin the partition walls) within 80 μm in the partition wall thicknessdirection (direction perpendicular to the partition wall) from theoutermost contour line of the partition wall toward the partition wallsurface. In addition, the same can be applied to the particle layer. Inaddition, the same can be applied to the case where the particles,particle assemblages, and particle layers are present together to formthe composite region. Further, the “height of the composite region”means the distance from the farthest point in the partition wallthickness direction (direction perpendicular to the partition wall)(point where the outermost contour line is farthest from the projectionline) with the outermost contour line of the partition wall as the baseto the outermost contour line.

As a specific measurement method of the “height of the compositeregion”, a resin-embedded polished cross section or a fracture surfaceis observed by a SEM, and an image analysis is performed for themeasurement. In the image analysis, the outermost contour line of thepartition wall is drawn, and then a line parallel to the outermostcontour line in the partition wall thickness direction (directionperpendicular to the partition wall) is drawn. Then, the line parallelto the outermost contour line is gradually raised toward the upstreamside (partition wall perpendicular direction side) for observation. Inthe observation visual field, the point where the particle assemblageseparates from the line parallel to the outermost contour line isobtained for the measurement with the distance from the outermostcontour line of the partition wall as the composite region height.

Specifically, the outermost contour line 17 having irregularity can beshown in FIG. 11. At least particles are deposited in the region of 80μm or less from the outermost contour line in the partition wall surfacedirection. More specifically, as shown in FIG. 12, the outermost contourmeans the contour obtained when the contour line forming the outermostcontour of the partition wall is connected to the point P where theprojection line is separated. Further, in the case that contour linesare separated from each other to form a pore, the supposition lineobtained by drawing the parallel line I parallel to the surface layerreference line H from the point P where the open pore surface of thepartition wall separates from the projection line and further drawing aperpendicular line from the point P to connect with the aforementionedparallel line I is referred to as the outermost contour line.Incidentally, the reference symbol J shown in the figure shows aprojection line to the surface layer reference line.

Incidentally, though the outermost contour line shown in FIG. 11 isdrawn as a supposition line like a belt, it is for the convenience ofdescription, and, needless to say, such a supposition line is not shownin the honeycomb filter of the present embodiment.

In the case, regarding the surface layer reference line, the “compositeregion depth” and “composite region depth rate” in the presentspecification mean the following content, respectively.

The “composite region depth” means the depth of entry of the particlesto be deposited from the aforementioned surface layer reference linetoward the down stream side in the partition wall thickness direction inthe partition wall surface layer having irregularity. The “compositeregion depth” can be measured by the following technique. In the firstplace, a sample obtained by subjecting the partition wall base materialto resin-embedded polishing is prepared in advance, and the surfacelayer reference line is obtained by an image analysis or the like in aSEM observation. Next, from the surface layer reference line, the depthof the entry of the particles deposited on the downstream side of thepartition wall is measured. Thus, the maximum entry depth in one visualfield of the SEM is determined as the composite region depth in themeasurement.

The “composite region depth rate” means the proportion of theaforementioned composite region depth with respect to the partition walldepth. Here, the “partition wall thickness” means the distance betweenthe partition wall surface on the upstream side and the partition wallsurface on the downstream side. More strictly speaking, it is shown bythe distance between the surface layer reference lines on the upstreamside and on the downstream side. For the measurement of the partitionwall thickness, a sample obtained by subjecting the partition wall basematerial to resin-embedded polishing is prepared in advance in the samemanner as in the measurement of the composite region depth. Further, byobtaining the surface layer reference lines on the upstream side and thedownstream side in the SEM observation of the polished face of thesample, the “composite region depth rate” can be measured.

Incidentally, each of the measurements of the “composite region depth”and the “composite region depth rate” is performed as follows. As shownin FIG. 3, measurement is performed at three to five points in total inthe central portion and outer peripheral portion in a cross sectionperpendicular to the axial direction with respect to the radialdirection in the central portions of the upstream portion (exhaust gasinflow side Z1), mid-stream portion (mid-stream portion Z2 (mid-streamregion Z2)), and the down stream portion (exhaust gas outflow side Z3)with respect to the axial direction of the honeycomb filter. The averagevalue of the measurement data at 9 to 15 points in total is determinedas the measurement value of the honeycomb filter to be measured. Theupstream potion, the mid-stream portion, and the downstream portion aretrisected, and the measurement is performed in the central portion ofeach section. Regarding the radial direction, the region on the centralside with respect to the center of the radius is determined as a centralportion, and the region on the outside with respect to the center of theradius is determined as the outer peripheral portion in the radius of across section, and the measurement is performed at three to five pointsof each of the regions. Here, the aforementioned “radial direction”means the outside direction in a cross section perpendicular to theaxial direction of the honeycomb filter and is not limited to themeaning of the words. This is because not only the case that the crosssection perpendicular to the axial direction of the honeycomb filter iscircular, but also the case that the cross section is oval and the casethat the cross section is irregular are included.

In addition, it is preferable that the composite region is formed in thepores formed in the surface layer of the partition walls and the poresin the partition walls in the range from the surface layer referenceline of a partition wall on the exhaust gas inflow side to 30% of thepartition wall thickness. This is because, when the particles depositedis above 30% in the partition wall thickness direction, the depositedparticles begin to clog the neck portions of the partition wall pores,and the possibility of causing pressure loss of the partition wallrises. That is, when the “neck portion” of a partition wall pore isclogged, exhaust gas cannot permeate the partition wall to make the flowof the exhaust gas into the adjacent cell though the partition walldifficult. This state raises the (inflow and outflow) pressure whenexhaust gas passes through the partition wall (make the gas permeabilitylow), and the stress applied to the partition wall increases. Therefore,the pressure loss of the partition wall is easily caused.

Here, the “[neck portion] of partition wall pore” means the region wherethe size of the pore is small in the distribution of pores in thepartition wall and region where the inner diameter of the duct line issmall. For example, the region is shown by the symbol N in FIG. 4A. Inaddition, “the deposited particles begin to clog the neck portions ofthe partition wall pores” means that the clogging of the neck portionsis increased by the formation of the composite region to narrow theexhaust gas passage by the clogging. Thus, when “the deposited particlesbegin to clog the neck portions”, the gas permeability falls to increasepressure loss.

Further, it is preferable that the composite region is formed in thepores formed in the surface layer of the partition walls and the poresin the partition walls from the surface layer reference line of thepartition wall on the exhaust gas inflow side to the depth up to 4 timesthe average pore diameter of the partition wall. When it is larger than4 times, the particles forming the composite region begin to clog a neckportion in the open pores and the pores in the partition walls, andpressure loss rises. When the clogging in neck portions of partitionwall pores increases, the pressure loss rises, which is not preferable.

Here, the phrase of “in the open pores formed in the surface layer ofthe partition walls and the pores in the partition walls to the depth upto 4 times the average pore diameter of the partition wall” means “inthe open pores formed in the region to the depth (partition wallthickness) of 4 times the average pore diameter of the partition wall orless in the surface layer of the partition walls in the partition wallthickness direction and the pores in the partition walls”. For example,when the average pore diameter of the partition wall is 15 μm, it means“in the open pores formed up to about 60 μm in the partition wallthickness direction and the pores in the partition walls”.

It is preferable that the partition walls have a porous structureconstituted of a pore-linked form and that the composite region has aporous structure constituted of a particle-liked form. When thepartition walls have a structure of a pore-linked form, there arepresent many forms where the pore size inside the partition walls islarger than the pore size in the surface layer of the pores exposed tothe surface of the partition walls. Therefore, forming of a compositeregion makes a state where the particles forming the composite regionenter the pores in the partition walls to be able to remarkably clog thepores in the partition walls. As a result, the rapid rise of thepressure loss incidence rate can be avoided. In addition, when thecomposite region is constituted of a particle-linked form, since thecontact points between the particles are small, linking of the passagebetween the particles is easily secured, and the possibility of causingthe rapid rise of the pressure loss incidence rate can be lowered.

In addition, it is preferable that the particles to be deposited in thepores formed in the surface layer of the partition walls and the poresin the partition walls are of the same material as that for thepartition walls. In the case that the particles to be deposited in thepores formed in the surface layer of the partition walls and the poresin the partition walls are formed of the same material as that for thepartition walls, not only the adjustment of durability and stress iseasy, but also the formation is simple, which is preferable. Further, aunit price of the product can be reduced, which is preferable. Here,“formed of the same material as that for the partition walls” meansthat, for example, in the case that the partition walls are formed ofcordierite or aluminum titanate, the particles formed of cordierite oraluminum titanate serving as the framework of the partition walls aredeposited.

In addition, it is preferable that the partition walls are formed ofcordierite or aluminum titanate. When the partition walls are formed ofcordierite or aluminum titanate, since they are materials of a reactionsintering type, a microstructure of a pore-linked form can be obtained.

In addition, it is also one of preferable embodiments that the particlesto be deposited in the pores formed in the surface layer of thepartition walls and the pores in the partition walls are bonded by thesintering of the particles. In the case that the particles are bondedtogether or the particles are bonded with the partition walls by thesintering, the form of the contact may easily become point contact to beable to sufficiently secure the space between the particles. Therefore,particularly under the conditions where the exhaust gas flow rate isextremely high upon driving at high rotation, the pressure lossincidence rate can be lowered furthermore remarkably.

[1-2] Honeycomb-Structured Body:

The substrate for the honeycomb structure in the present embodiment is ahoneycomb-structured substrate provided with a plurality of cellsseparated by partition walls 4 of porous ceramic having numeral poresand functioning as exhaust gas passages as shown in FIGS. 1 to 3. Thehoneycomb-structured substrate is constituted as a honeycomb filterwhere the partition walls 4 of the cells 3 each have the upstream layer13 on the exhaust gas upstream side and the downstream layer 15 on thedownstream side. Incidentally, a catalyst may be loaded on the honeycombfilter as necessary to obtain a catalyst-loaded filter.

In addition, plugging portions may be formed to alternately plug theopen end portions 11 a on one side and the open end portions 11 b on theother side of plural cells.

Incidentally, the entire shape of the honeycomb structure is notparticularly limited and may be a quadrangular columnar shape, atriangular columnar shape, or the like as well as a circular cylindricalshape as shown in FIGS. 1 and 2.

In addition, examples of the shape of the cells (cell shape in across-section perpendicular to the cell formation direction) thehoneycomb-structured substrate includes a square shown in FIG. 1, ahexagon, and a triangle. However, the shape is not limited to such ashape, and known cell shapes can widely be included. A more preferablecell shape is a circle or a polygon having four or more angles. Thereason why a circle or a polygon having four or more angles ispreferable is because the thickness of the catalyst layer can be madeuniform by decreasing the thick catalyst in a corner portion in the cellcross section. Above all, in consideration of cell density, open ratioand the like, a hexagonal cell is suitable.

Though there is no particular limitation on the density of the cells thehoneycomb-structured substrate is provided with, in the case of use as acatalyst-loaded filter of the present embodiment, it is preferably 0.9to 233 cells/cm². In addition, the thickness of partition walls ispreferably 20 to 2000

In addition, the porosity of the partition walls of thehoneycomb-structured substrate is provided with is 35 to 75%. When theporosity of the partition walls is lower than 35%, the gas permeabilityof the partition walls remarkably falls. The pressure loss incidencerate of the partition walls (increase in pressure loss incidence in thepartition walls) to the soot deposition amount (soot deposition increaseamount) shows a tendency to increase in a linear form. However, in astate that soot does not deposit because of remarkably low gaspermeation, the pressure loss incidence rate of the partition wallsshows a tendency of further rise, which is not preferable. In addition,when the porosity is higher than 75%, the material strength falls, and acrack may be caused upon canning, which is not preferable.

Incidentally, it is preferable that the porosity of the composite regionis lower than that of the partition wall substrates and that theporosity of the layer of the particle assemblages depositing on thepartition walls is higher than that of the composite region. Such aconstitution enables to rise the PM trapping efficiency of the honeycombfilter and to suppress the pressure loss incidence rate of the partitionwalls.

More specifically, setting can be performed in such a manner that theporosity of the partition walls is 35 to 75%, that the porosity of thecomposite region formed in the partition walls on the downstream sidewith respect to the surface layer reference line is lower than that ofthe partition walls by 5 to 30%, that the porosity of the particle layerof particle assemblages deposited on the upstream partition wall surfacelayer side with respect to the surface layer reference line (upstreampartition wall surface side with respect to the surface layer referenceline) is larger than that of the composite region formed in thepartition walls on the downstream side with respect to the surface layerreference line by 5 to 40%, and that the porosity of the particle layerof particle assemblages deposited on the partition walls is 50 to 90%.When the porosity of the composite region formed on the partition wallson the downstream side with respect to the surface layer reference lineis lower than the porosity of the partition walls by 5 to 30%, thenecessary and sufficient exhaust gas passages can be secured, and thesufficient soot trapping performance can be secured. By securing thesoot trapping performance, soot can be inhibited from passing throughthe composite region. By inhibiting the soot from passing through thecomposite region, the pressure loss incidence rate of the partitionwalls upon soot deposition due to soot deposition in the substrate pores(pores of the partition walls) in the region below the composite region.

That is, when the fall of the porosity of the composite region incomparison with the partition walls outside the composite region issmaller than 5%, the composite region is not formed sufficiently.Therefore, soot passes through the composite region and deposits in thepores of the partition walls in the region below of the compositeregion. When soot deposits in the pores of the partition walls in thisregion, the pressure loss incidence rate of the partition walls rises toa large extent. In addition, when the fall of the porosity of thecomposite region in comparison with the partition walls outside thecomposite region is larger than 30%, the composite region is densified.As a result, the gas permeability falls to raise the pressure lossincidence rate of the partition walls to a large extent particularly inthe high flow rate region (region where exhaust gas passes at high flowrates). In addition, when the porosity in the composite region above thesurface layer reference line is higher than 40% with respect to theporosity in the composite region below the surface layer reference line,the change in porosity in the vicinity of the surface layer referenceline becomes too large. As a result, since the bonding points betweenthe particles decrease, peeling of a particle or a particle assemblageis easily caused in the vicinity of the surface layer reference line. Inaddition, when the porosity of the particle assemblage deposited in thecomposite region above the surface layer reference line in the compositeregion above the surface layer reference line or the particle layer ofthe particle assemblage deposited is smaller than 50%, since the flowrate of the soot passing through the pores upon the soot deposition inthe gaps (space) between the particles is high, the pressure lossincidence rate of the partition walls rises to a large extent. Inaddition, when the porosity of the particle assemblages deposited in thecomposite region above the surface layer reference line or the particlelayer of the particle assemblages is higher than 90%, the bonding pointsbetween the particles decrease extremely in the same manner as describedabove. As a result, the bonding strength of the particle assemblagefalls, and peeling may be caused when it is exposed to high flow rateconditions (in the case that exhaust gas passes at high flow rates).

Incidentally, the porosity of the composite region is binarized in theimage analysis of the SEM observation photograph of a resin-embeddedpolished surface, and the rate of the gaps (spaces) between theparticles is determined as the porosity.

In addition, the “average pore diameter” and “porosity” of the partitionwall substrates in the present specification mean the average porediameter and the porosity measured by mercury penetration method. Theaverage pore diameter and the porosity of the particle assemblagedeposited in the composite region or on the partition walls are measuredby appropriately adding the measurement evaluation by subjecting animage taken by a SEM (scanning electron microscope) to the binarizationtreatment. Specifically, the “average pore diameter” of the partitionwall substrate is determined by measuring the partition wall substrateby a mercury penetration method. When the pore distribution obtained bythe measurement has two peaks, the pore diameter having the largest porecapacity of the distribution having a larger pore size is determined asthe average pore diameter of the partition wall substrate. On the otherhand, in the case that the pore distribution obtained has only one peakand that the pore distribution of the partition wall substrate cannot beidentified, a desired region of a cross section perpendicular to theaxial direction of the partition wall is subjected to resin-embeddedpolishing, the SEM (scanning electron microscope) observation isperformed in the visual field of 100 to 1000 magnifications, and theimage obtained is binarized to measure the average pore diameter of thepartition wall substrate. In the same manner, the “porosity” of thepartition wall substrate is measured in such a manner that a desiredregion of a cross section perpendicular to the axial direction of thepartition wall is subjected to resin-embedded polishing, the SEM(scanning electron microscope) observation is performed in the visualfield of 100 to 1000 magnifications, and the image obtained is binarizedto obtain the porosity from the area ratio of the gaps to the particlesin one visual field. In addition, the “particle diameter” of thepartition wall substrate is measured by the SEM image analysis as in theaforementioned measurements of the pore size and the porosity in thecomposite region. The maximum inscribed circle distribution is obtainedwith respect to the outermost contour of the particles constituting thesubstrate, and the diameter distribution of the maximum inscribed circleis obtained. The maximum inscribed circle having a diameter smaller than1 μm is determined that it is not a particle region, and D50 in themaximum inscribed circle distribution is determined as the averageparticle diameter of the substrate.

Incidentally, “D50” means the size of the “50th” particle when particlediameters measured are aligned in order of size to determine the largestparticle as the 100th particle.

In addition, the partition walls which the honeycomb-structuredsubstrate is provided with have an average pore diameter of 5 to 40 μm.Preferably, the partition walls have an average pore diameter of 10 to20 μm. When the average pore diameter is smaller than 5 μm, gaspermeability is prone to be lowered remarkably to make pressure losswith no soot deposition very high. When it is larger than 40 μm, sincePM can pass through the space between the partition walls and theparticles deposited in the composite region even if the composite regionis formed by depositing particles, the PM trapping efficiency in thehoneycomb filter is not sufficient.

Incidentally, it is preferable to have a relation where the average porediameter of the composite region is made smaller than the average porediameter of the partition walls and where the particle layer formed ofparticle assemblages deposited on the partition walls is made smallerthan the average pore diameter of the composite region. Suchconstitution enables to raise the PM trapping efficiency in thehoneycomb filter and suppress the pressure loss incidence rate of thepartition walls. For example, the setting may be performed in such amanner that the average pore diameter of the partition walls is 10 to 20μm, that the average pore diameter of the composite region is 5 to 10μm, that the average pore diameter of the particle layer formed ofparticle assemblages deposited on the partition walls is 1 to 5 μm, andthat each of the average pore diameter of the partition walls, theaverage pore diameter of the composite region, and the average porediameter of the particle assemblages deposited on the partition wallsand particle layers has the size relation among the aforementioned threeaverage pore diameters.

Further, it is preferable that the thickness of the partition wallswhich the honeycomb-structured substrate is provided with is 200 to 600μm. When it is smaller than 200 μm, soot deposited upon regenerationeasily causes extraordinary combustion. Therefore, the internaltemperature of the honeycomb filter or the internal temperature of theDPF at the time when the honeycomb filter is used as DPF rises, and acrack may be caused. On the other hand, when it is larger than 600 μm,the hydraulic diameter becomes too small, and the pressure lossincidence rate of the partition walls may rise.

Further, in a honeycomb filter of the present embodiment, it ispreferable to have a structure where open end portions on one side andopen end portions on the other side of the plural cells of thehoneycomb-structured substrate are alternately plugged. For example, asshown in FIG. 3, the structure may be formed in such a manner that ahoneycomb-structured body having plural cells 3 separated by partitionwalls 4 of porous ceramic having numeral pores and functioning asexhaust gas passages is employed as a substrate and that the one sideopen end portions 11 a and the other side open end portions 11 b of theplural cells 3 of the honeycomb-structured body are alternately pluggedby plugging portions 8. In such a honeycomb-structured body, the exhaustgas G₁ is sent from the opening exhaust gas inflow cells 3 in theexhaust gas inflow side end face 7 a, particulates in the exhaust gas G₁are trapped by the partition walls 4 when the exhaust gas G₁ passesthough the partition walls 4. Further, the exhaust gas G₂ from which theparticulates are removed moves toward the exhaust gas outflow side endface 7 b and is discharged outside of the honeycomb filter from theopening exhaust gas outflow cells 3.

In addition, an oxidation catalyst, other catalysts, and a purificationmaterial (hereinbelow, appropriately referred to as “catalyst and thelike”) may be loaded on a part of or the entire partition walls of thehoneycomb-structured substrate and/or a part of or the entire compositeregion. That is, the catalyst and the like may be loaded on a part of orthe entire partition walls, and the catalyst and the like may be loadedon a part of or the entire composite region. Further, a catalyst may beloaded on a part of or the entire partition walls and a part of or theentire composite region. In addition, for example, there may be loaded aNOx adsorber catalyst having an alkali metal (Li, Na, K, Cs, etc.) or analkali earth Metal (Ca, Ba, Sr, etc.), a ternary catalyst, an auxiliarycatalyst represented by an oxide of cerium (Ce) and/or zirconium (Zr),HC (hydrocarbon) adsorber, or the like.

For example, the PM removal catalyst may contain Ce and at least onerare earth metal, alkali earth metal, or transition metal.

Here, the rare earth metal can be selected from, for example, Sm, Gd,Nd, Y, Zr, Ca, La, and Pr.

In addition, the alkali earth metal contained in the PM removal catalystcan be selected from, for example, Mg, Ca, Sr, and Ba.

In addition, the transition metal contained in the PM removal catalystcan be selected from Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, V, and Cr.

In addition, there is no particular limitation on the loading method ofthe catalyst component such as an oxidation catalyst and a NOx adsorbercatalyst. An example of the method is a method where, after thepartition walls of the honeycomb-structured body are subjected to washcoating with a catalyst solution containing a catalyst, it is subjectedto a thermal treatment at high temperature for baking. Incidentally, theaverage pore diameter can be adjusted to be a desired value bycontrolling the particle size, the compounding ratio, and the like inthe framework particles in the ceramic slurry; the porosity can beadjusted to be a desired value by controlling the particle size of theframework particles, the amount of the pore former, and the like in theceramic slurry; and the thickness of the coat layer of the partitionwalls can be adjusted to be a desired value by controlling concentrationof the ceramic slurry, time required for the membrane formation, and thelike.

Incidentally, since the catalyst component such as an oxidation catalystand a NOx adsorber catalyst is loaded in a highly dispersed state, it ispreferable to load the catalyst component on the partition walls and thelike of the honeycomb-structured body after once loading it on a thermalresistant inorganic oxide having a large specific surface area such asalumina in advance.

In addition, the aforementioned PM removal catalyst can be loaded by,for example, a method where catalyst slurry is loaded inside the poresof the partition walls by applying a conventionally knowncatalyst-loading method such as dipping or suction, followed by dryingand firing.

An example of the production method of a honeycomb-structured body isthe following method. However, without limiting to the production methodof a honeycomb-structured body, a known production method of ahoneycomb-structured body can be employed.

In the first place, the clay for forming a honeycomb filter is formed.In the first place, a cordierite-forming raw material is prepared as amaterial for kneaded clay. The cordierite-forming raw material used forthe manufacturing of a honeycomb filter of the present embodimentcontains an alumina source, a silica source, and a magnesia source andis obtained by mixing plural raw material powders in such a manner thatthe composition after firing becomes a theoretical composition(2MgO.2Al₂O₃.5SiO₂). Though the material contains cordierite as the maincrystal, it may contain other crystal phases such as mullite, zircon,aluminum titanate, clay bond silicon carbide, spinel, indiarite,sapphirine, corundum, and titania. In addition, these crystal phases maybe contained alone as one kind or as two or more kinds.

In the present specification, examples of the “alumina source” includealumina, aluminum hydroxide, activated alumina, and boehmite(Al₂O₃.H₂O). In addition, particles of kaolin (Al₂O₃.2SiO₂.2H₂O) ormullite (3Al₂O₃.2SiO₂) can be used as a substance playing roles of thealumina source and the silica source.

Examples of the silica source include particles of silica, a compositeoxide containing silica, and a substance converted into silica byfiring. Specifically, besides the aforementioned talc (3MgO.4SiO₂.H₂O)functions as a silica source, particles of silica (SiO₂) includingquartz, kaolin (Al₂O₃.2SiO₂.2H₂O), calcined kaolin, and mullite(3Al₂O₃.2SiO₂). Incidentally, the calcined kaolin is obtained bycalcining kaolin (raw kaolin) produced as a mineral at a predeterminedtemperature, for example 1000 to 1100° C.

As the magnesia source, there may be used particles of magnesia, acompound oxide containing magnesia, a substance converted into magnesiaby firing, or the like. Besides the aforementioned talc (3MgO.4SiO₂.H₂O)functions as a magnesia source, for example, particles of magnesite(MgCO₃) or the like can be used. Incidentally, in the presentembodiment, it is preferable to use talc particles as the magnesiasource.

Incidentally, in a honeycomb-structured body of the present embodiment,it is preferable to use a cordierite-forming raw material mixed in sucha manner that the composition after firing becomes a theoreticalcomposition (2MgO.2Al₂O₃.5SiO₂).

In addition, there is no particular limitation on the particle size andthe average particle diameter of the talc particles. For example, theaforementioned particle size and the average pore diameter canappropriately be selected according to the aimed function, specifically,porosity, pore distribution, and the like.

Incidentally, the “average particle diameter” here means a value of 50%particle diameter measured with a laser diffraction/scattering particlesize measurement apparatus (e.g., trade name of LA-910 produced byHoriba, Ltd.) with a light scattering method as the measurementprinciple. Incidentally, the measurement is carried out in a state wherethe raw material is completely dispersed in water.

In a honeycomb filter of the present embodiment, it is preferable thatthe cordierite-forming raw material contains raw material particles ofkaolin, calcined kaolin, silica, and alumina source. Such constitutionenables to easily adjust the porosity, the pore distribution, and thelike. Incidentally, these other raw material particles are contained atthe rate where the composition after firing becomes a theoreticalcomposition (2MgO.2Al₂O₃.5SiO₂) of cordierite.

Incidentally, as the alumina source, there may suitably be employedalumina, aluminum hydroxide, activated alumina, boehmite, or the like.The alumina source can appropriately be selected according to thepurpose of use.

In addition, though there is no particular limitation on the averageparticle diameter of the raw material particles serving as the silicasource, there are suitably used quartz particles (silica particles)having an average particle diameter of about 5 to 50 μm, kaolinparticles having an average particle diameter of about 2 to 10 μm,calcined kaoline particles having an average particle diameter of about1 to 5 μm, and mullite particles having an average particle diameter of2 to 20 μm.

Next, a dispersion medium such as water is added to thecordierite-forming raw material obtained as described above, and theyare mixed together and kneaded to obtain kneaded clay.

Though the dispersion medium added to the cordierite-forming rawmaterial may be water, a mixed solvent of water and an organic solventsuch as alcohol, or the like, in particular, water can suitably be used.In addition, when the cordierite-forming raw material and the dispersionmedium are mixed together and kneaded, additives such as a pore former,an organic binder, and a dispersant may further be added.

Examples of the pore former include carbon such as graphite, flour,starch, phenol resin, poly(methyl methacrylate), polyethylene, andpolyethylene telephthalate. Of these, a microcapsule formed of anorganic resin such as acrylic resin can particularly suitably be used.

As the organic binder, for example, hydroxypropylmethyl cellulose,methyl cellulose, hydroxyethyl cellulose, carboxylmethyl cellulose, orpolyvinyl alcohol can suitably be used. As the dispersant, a substancehaving a surface-active effect, such as ethylene glycol, dextrin, fattyacid soap, or polyalcohol can suitably be used.

Incidentally, mixing and kneading of the cordierite-forming raw materialand the dispersion medium may be performed by a known mixing andkneading methods. However, the mixing is preferably performed by amethod of stirring with a shearing force by the use of a mixer capableof rotating a stirrer blade at a high speed of 500 rpm or more(preferably 1000 rpm or more) and excellent in the stirring force andthe dispersion force. Such a mixing method enables to crush and clear upaggregated masses of microparticles contained in each of the rawmaterial particles.

The mixing can be performed by the use of a conventionally known mixersuch as a sigma kneader or a ribbon mixer. In addition, the kneading canbe performed by the use of a conventionally known kneader such as asigma kneader, a Banbury mixer, or a screw-type extrusion kneader. Inparticular, it is preferable to use a kneader provided with a vacuumpressure-reduced apparatus (e.g., vacuum pump) (so-called vacuum kneaderor biaxial continuous kneading extruder) because kneaded clay having fewdefects and good formability can be obtained.

The resultant kneaded clay is formed by a forming method such asextrusion forming to be able to obtain a honeycomb formed body having aplurality of cells separated and formed by partition walls. As theextrusion forming, a method of using a die having desired cell shape,partition wall thickness, and cell density is suitable.

Next, the honeycomb formed body is dried, and plugging portions wereformed by plugging both the end portions of the dried honeycomb formedbody to obtain a honeycomb dried body. The method of drying is notparticularly limited. A conventionally known method such as hot airdrying, microwave drying, dielectric drying, pressure-reduced drying,vacuum drying, or freeze drying may be employed. Of these, the dryingmethod where hot air drying is combined with microwave drying ordielectric drying is preferable in that the entire formed body can bedried quickly and uniformly.

As a method for forming plugging portions, plugging slurry is stored ina storage container. Then, an end portion having the aforementioned maskapplied thereto is immersed in the slurry in the storage container tofill the plugging slurry into the opening portions of the cells havingno mask, thereby forming plugging portions. A mask is applied to theother end portions of the cells plugged in the one end portions, andplugging portions are formed in the same manner as in the formation ofplugging portions on the aforementioned one end portions. Thus, theother end portions of the cells which are not plugged in theaforementioned one side end portions are plugged to have a structurewhere the cells are alternately plugged in the checkerwise pattern onthe other end portions. In addition, the plugging may be performed afterthe honeycomb fired body is formed by firing the honeycomb formed body.

Incidentally, when the same material as the honeycomb segment rawmaterial is used as the plugging material, the expansion coefficientupon firing can be made the same as that of the honeycomb segments toimprove durability, which is preferable.

Next, the resultant honeycomb dried body is fired to obtain ahoneycomb-structured body. Since the firing conditions (temperature andtime) are different depending on the kind of the raw material, suitableconditions may be selected in accordance with the kind. For example,firing at a temperature of about 1410 to 1440° C. for 3 to 10 hours ispreferable. When the firing conditions (temperature and time) are belowthe aforementioned ranges, cordierite crystallization of the frameworkraw material particles tends to be insufficient. On the other hand, whenthey are above the aforementioned ranges, formed cordierite tends tomelt.

Incidentally, it is preferable to perform an operation (calcination) ofremoving the organic matter (pore former, organic binder, dispersant,etc.) in the honeycomb dried body before firing or in the process ofraising temperature for firing because the removal of the organic mattercan be facilitated. The combustion temperature of the organic binder isabout 200° C., and the combustion temperature of the pore former isabout 300 to 1000° C. Therefore, the calcination temperature may beabout 200 to 1000° C. Though there is no particular limitation on thecalcination time, it is generally about 10 to 100 hours.

Incidentally, a honeycomb filter of the present invention can suitablybe used as a diesel particulate filter (DPF) for trapping particulatematter (PM) discharged from a diesel engine.

[2-1] First Production Method of the Present Invention:

As an embodiment of the first production method of a honeycomb filter ofthe present invention, it is preferable that the method includes thesteps of: forming a honeycomb formed body by subjecting a forming rawmaterial containing a ceramic raw material to extrusion forming andforming plugging portions in one side open end portions and the otherside open end portions of the other cells of the honeycomb formed body,firing the honeycomb formed body to form a honeycomb fired body,supplying particles having an average particle diameter smaller than theaverage pore diameter of the partition walls from the one side open endportions of the honeycomb fired body by a solid-gas two-phase flow, and,at least in the pores formed on the surface layer of the partition walland the pores in the partition walls, forming a composite region bydepositing particles having an average particle diameter smaller thanthe average pore diameter of the partition walls in a surface layerportion of the partition walls on the exhaust gas inflow side; whereinthe partition walls have an average pore diameter of 5 to 40 μm and aporosity of 35 to 75%, the particles deposited has an average particlediameter of 1 to 15 μm, and the composite region has a height of 80 μmor less with respect to the partition wall surface direction from theoutermost contour line of the partition walls. By such production, thecontact area between the deposited particles is decreased, and securingof the gaps between the particles, that is, passages becomes easy, andpressure loss can be suppressed.

Specifically, in the first place, as described above, the forming rawmaterial containing a ceramic raw material is subjected to extrusionforming to form a honeycomb formed body provided with partition wallsseparating and forming plural cells functioning as fluid passages andextending over from one side end face to the other side end face. Next,a honeycomb-structured body where plugging portions are formed in oneside open end portions and the other side open end portions of the othercells of the honeycomb formed body is prepared.

Further, a honeycomb-structured body is subjected to firing (mainfiring) to form a honeycomb fired body. Since the firing conditions(temperature and time) here are different depending on the kind of theraw material, suitable conditions may be selected in accordance with thekind. For example, the firing temperature in the case of firing in theAr inert atmosphere is generally about 1410 to 1440° C., and firing timeis 3 to 10 hours. However, the conditions are not limited to these.

Further, from one side open end portions of the aforementioned honeycombfired body, particles having the average particle diameter smaller thanthe average pore diameter of the partition walls are supplied by asolid-gas two-phase flow to deposit the particles having the averageparticle diameter smaller than the average pore diameter of thepartition walls at least in the pores formed in the surface layer of thepartition walls and the pores in the partition walls. Thus, a honeycombfilter having at least the composite region can be obtained.

For example, as a method for depositing the particles having an averageparticle diameter smaller than the average pore diameter of thepartition walls by supplying them by a solid-gas two-phase flow, thereis a method where the air containing particles to be deposited in thepores formed in the surface layer of the partition wall and the pores inthe partition walls is sent into the honeycomb filter (DPF) from theexhaust gas inlet side end face (end face on the exhaust gas inlet sideof the DPF) of the honeycomb filter. Such a method enables to form thecomposite region by gradually depositing particles in the open poresformed in the partition walls of the cells (inlet cells) where the inletof the gas is open and the pores in the partition walls and on thepartition walls. Further, by sucking the particles from the exhaust gasinlet side end face (exhaust gas inlet side end face of the DPF) of thehoneycomb filter, the particles are introduced into the partition wallpores to be able to further stabilize the deposition state.

Incidentally, upon depositing particles in the open pores and the poresin the partition walls as necessary, it is preferable to supply theparticles having an average particle diameter smaller than the averagepore diameter of the partition walls by a solid-gas two-phase flow bysetting the open end portion where the exhaust gas flows in of thehoneycomb fired body after the honeycomb formed body is fired to facedownward to form a honeycomb fired body. This makes deposition of theparticles easy on the surface layer portions of the partition walls onthe exhaust gas inflow side and on the partition wall surface layerportions in a desired region, thereby making formation easy.

Further, it is possible that plural honeycomb fired bodies each having acomposite region formed therein are subjected to grinding to obtain acircular shape, an oval shape, a race track shape, or the like, followedby coating the outer periphery with a coating material.

[2-2] Second Production Method of the Present Invention:

As an embodiment of the second production method of a honeycomb filterof the present invention, it is also preferable that the method includesthe steps of: forming a honeycomb formed body by subjecting a formingraw material containing a ceramic raw material to extrusion forming andforming plugging portions in one side open end portions and the otherside open end portions of the other cells of the honeycomb formed body,firing the honeycomb formed body to form a honeycomb fired body,supplying particles having an average particle diameter smaller than theaverage pore diameter of the partition walls from the one side open endportions of the honeycomb fired body by a solid-gas two-phase flow, atleast in the pores formed in the surface layer of the partition wallsand the pore in the partition walls, forming a composite region bydepositing particles having an average particle diameter smaller thanthe average pore diameter of the partition walls in a surface layerportion of the partition walls on the exhaust gas inflow side, andfurther performing a thermal treatment; wherein the partition walls havean average pore diameter of 5 to 40 m and a porosity of 35 to 75%, theparticles deposited has an average particle diameter of 1 to 15 μm, andthe composite region has a height of 80 μm or less with respect to thepartition wall surface direction from the outermost contour line of thepartition walls. That is, it is desirable that, after the step forming adesired composite region, a thermal treatment step is further performedto produce a honeycomb filter. By such a thermal treatment, theparticles to be deposited, particle assemblages, the particle layers,and/or surfaces of the partition walls can be bonded sufficiently, anddurability of the composite region can be improved.

Incidentally, in the second production method of a honeycomb filter ofthe present invention, a series of steps from the step ofextrusion-forming a forming raw material containing a ceramic rawmaterial to the step of depositing the particles by the solid-gastwo-phase flow on the honeycomb fired body are the same as in the firstproduction method of a honeycomb filter of the present invention.Therefore, here, the thermal treatment step after the particles aredeposited will be described, and regarding a series of the stepdescribed above, please refer to the first production method of ahoneycomb filter of the present invention.

A honeycomb filter having a composite region formed in theaforementioned manner is further subjected to a thermal treatment. Thethermal treatment is performed for bonding the particle assemblageand/or the particle layers to the particle layers, and the surfaces ofthe aforementioned partition walls and is different from the calcinationand the main firing for obtaining a honeycomb fired body.

Incidentally, as examples of the thermal treatment conditions(temperature and time), the maximum temperature is 1200 to 1350° C. inan ambient atmosphere, and the time for keeping the target maximumtemperature is 30 to 300 minutes.

Thus, it is also possible that, after the aforementioned particleassemblages, and/or the particle layers, and the surfaces of theaforementioned partition walls are bonded together, further, grinding isperformed to obtain a circular shape, an oval shape, a race track shape,or the like, and, further, coating the outer periphery with a coatingmaterial is performed.

Incidentally, after a product is completed, a catalyst coating step isperformed to obtain a catalyst-loaded honeycomb filter in both the firstproduction method and the second production method of a honeycomb filterof the present invention. The catalyst distribution, composition, andthe like of the catalyst used in the catalyst coating step are as shownin [0091] to [0095], and the catalyst coat method is as shown in [0096]to [0098].

[2-3] Third Production Method of the Present Invention:

As an embodiment of the third production method of a honeycomb filter ofthe present invention, it is also desirable that the method includes thesteps of: forming a honeycomb formed body by subjecting a forming rawmaterial containing a ceramic raw material to extrusion forming andforming plugging portions in one side open end portions and the otherside open end portions of the other cells of the honeycomb formed body,firing the honeycomb formed body to form a honeycomb fired body, loadinga catalyst on the partition walls of the honeycomb fired body to obtaina catalyst-loaded honeycomb-structured body, supplying particles havingan average particle diameter smaller than the average pore diameter ofthe partition walls from the one side open end portions of thecatalyst-loaded honeycomb-structured body by a solid-gas two-phase flow,at least in the pores formed in the surface layer of the partition walland the pores in the partition walls, forming a composite region bydepositing particles having an average particle diameter smaller thanthe average pore diameter of the aforementioned partition walls in asurface layer portion of the partition walls on the exhaust gas inflowside, and further performing a thermal treatment; wherein the partitionwalls have an average pore diameter of 5 to 40 μm and a porosity of 35to 75%, the particles deposited have an average particle diameter of 1to 15 μm, and the composite region has a height of 80 μm or less withrespect to the partition wall surface direction from the outermostcontour line of the partition walls. Thus, since the composite region isformed after the catalyst is coated, there is no substantial depositionof a catalyst in the composite region. Therefore, the clogging of thegaps (spaces) between the particles in the composite region is notcaused substantially. As a result, there is little concern about therise of the pressure loss incidence rate of the partition walls. Inaddition, upon coating the catalyst, it is not necessary to payattention to avoiding the clogging in the composite region with thecoating of a catalyst in the composite region. Therefore, therestriction of the catalyst coating step is small, and catalyst coatingcan be performed at low costs.

In the first place, in the third production method of a honeycomb filterof the present invention, a series of steps from the step of subjectinga forming raw material containing the ceramic raw material to extrusionforming to the step of obtaining a honeycomb fired body are performed inthe same manner as in the first production method of a honeycomb filterof the present invention. Next, a catalyst is coated on the honeycombfired body (segments because they are not yet bonded). Incidentally, thecatalyst distribution, component, and the like of the catalyst used inthe catalyst coating step are as shown in to [0095], and the catalystcoat method is as shown in [0096] to [0098].

Further, after the catalyst is coated, the composite region is formed inthe same manner as in the second production method of a honeycomb filterof the present invention on the honeycomb fired body with a catalystcoating (with a catalyst). Then, through the thermal treatment step inthe same manner as in the second production method of a honeycomb filterof the present invention, a catalyst-loaded honeycomb filter can beproduced. Further, grinding may be performed to obtain a circular shape,an oval shape, a race track shape, or the like, followed by coating theouter periphery with a coating material to produce a honeycomb filterwith a catalyst.

Incidentally, regarding the catalyst coating method in the thirdproduction method of the present invention, the following catalystcoating method may be employed besides the catalyst coating method (see[0096] to [0098]) described above. For example, after catalyst slurry iscoated by dipping, suction, or the like, surplus slurry is blown away byair blow. Then, without the drying step, particles are deposited in awet state after the air blow unlike the conventional method where thedrying step follows. Then, a thermal treatment step including both acatalyst-drying step and a thermal treatment step for forming thecomposite region is performed. By employing such a catalyst coatingmethod, the treatment steps in catalyst coating can be reduced to beable to plan the reduction in costs. Incidentally, as the thermaltreatment conditions in a thermal treatment step including both acatalyst-drying step and a thermal treatment step for forming thecomposite region, the maximum temperature is 450 to 750° C. in anambient atmosphere, and the time for keeping the target maximumtemperature is 30 to 180 minutes.

Further, it is also preferable that, in addition to the third productionmethod of a honeycomb filter of the present invention, the methodincludes the steps of: supplying particles having an average particlediameter smaller than the average pore diameter of the partition wallsfrom one side open end portion of the honeycomb fired body by asolid-gas two-phase flow, and simultaneously, sucking the particles fromthe other open end portions of the honeycomb fired body to deposit theparticles in the pores formed in the partition walls on the exhaust gasinflow side to form a composite region. By thus sucking the particlesfrom the downstream side (the other open end portion side of thehoneycomb fired body) simultaneously with sending the carrier aircarrying the particles, particles can stably be deposited on thehoneycomb fired body in a short period of time.

EXAMPLE

Hereinbelow, the present invention will be described more specificallyby Examples. However, the present invention is by no means limited tothese Examples. Incidentally, “part” and “%” in the following Examplesand Comparative Examples mean mass part and mass % unless otherwisenoted. In addition, the various evaluations and measurements in Exampleswere carried out by the following methods.

[1] Full Load Pressure Loss:

In order to evaluate the pressure loss in the state of no sootdeposition, a DPF was mounted on a 2.2 L engine, and, after the enginewarm up for five minutes, a full load state at 4000 rpm was kept forfive minutes to measure the pressure loss on the front and back of thehoneycomb filter (DPF) at that time.

[2] Pressure Loss with Soot

In order to evaluate the pressure loss at the time of soot deposition, aDPF is mounted on the same engine, and, with constantly depositing sootwith 200 rpm×50 Nm, the behavior of the pressure loss rise was measured.After the test, the weight was measured to confirm the deposited sootamount.

[3] Trapping Efficiency:

Upon measuring the pressure loss with soot of [2], the soot amount onthe front and back of the DPF (gas inlet side and gas outlet side of theDPF) right after the DPF was mounted on the engine was measured with theSMPS (Scanning Mobility Particle Sizer produced by TSI Incorporated) tocalculate the trapping efficiency of the DPF.

[4] Isostatic Strength Test:

The DPF was covered with a rubber cover lest water should enter theinside of the DPF, and hydrostatic pressure was applied to the DPF inwater to measure the pressure where the DPF was destroyed.

Example 1

A cordierite-forming raw material was prepared by mixing 40 mass % oftalc particles, 15 mass % of kaolin particles (average particle diameterof 7 μm, BET specific surface area of 7 m²/g), 18 mass % of calcinedkaolin particles (average particle diameter of 3 μm, BET specificsurface area of 10 m²/g), 5 mass % of silica particles (average particlediameter of 4 μm, BET specific surface area of 3 m²/g), 13 mass % ofalumina particles (average particle diameter of 4 μm, BET specificsurface area of 2 m²/g), and 9 mass % of aluminum hydroxide (averageparticle diameter of 2 μm, BET specific surface area of 15 m²/g). To 100parts by mass of the cordierite-forming raw material prepared above wereadded 6 parts by mass of organic binders (methyl cellulose,hydroxypropylmethyl cellulose), 0.5 parts by mass of surface activeagent (sodium stearate), and 30 parts by mass of water, and they wereput in a mixer and mixed together for three minutes to obtain a wetmixture. The wet mixture was put in a screw-type extrusion kneader andkneaded to produce kneaded clay having a circular cylindrical shape. Thekneaded clay was put in an extruder and extrusion-formed to obtain ahoneycomb formed body. After the honeycomb formed body was subjected todielectric drying and hot air drying, both the end faces were cut tohave a predetermined size to obtain a honeycomb dried body. Plugging wasperformed for the honeycomb dried body obtained above, and then firingwas performed at 1420 to 1440° C. for five hours.

From the open end portion on the exhaust gas inflow side of thehoneycomb fired body obtained above, cordierite particles having anaverage particle diameter of 3 μm were supplied by a solid-gas two-phaseflow to deposit the cordierite particles having an average particlediameter of 3 μm in the open pores formed by the partition walls and/orthe gap between the particles in the surface layer portion of thepartition walls on the exhaust gas inlet side to form a compositeregion. Next, a thermal treatment was performed at the maximumtemperature, of 1300° C. with the maximum temperature keeping time oftwo hours to bond the cordierite particles together and bond thecordierite particles and the partition walls. Thus, there was obtainedhoneycomb-structured body (composite region-formed body) having a ribthickness (partition wall thickness) of 300 a cell pitch of 1.47 mm, aporosity of 41%, an average pore diameter of 14 μm, as partition wallproperties and an average particle diameter of 3 μm, a composite regiondepth (composite region thickness in the partition wall thicknessdirection) of 10 μm, a composite region depth rate (rate of thecomposite region depth with respect to the partition wall thickness) of3.3%, and a distance from the outermost contour line of 20 μm as thecomposite region/layer properties. Further, the peripheral face wascovered with an outer periphery coat layer formed of the same materialas that for the honeycomb formed body, followed by drying for hardeningto obtain a circular columnar honeycomb-structured body having adiameter of 144 mm, a length of 152 mm, and a cell density of 46.5cells/cm².

Next, a catalyst was loaded on the partition walls of thehoneycomb-structured body obtained above. In the first place, there waspreviously prepared slurry of a catalyst containing alumina, platinum,and ceria based material at a proportion of 7:1:2 (mass ratio) with theceria based material containing Ce, Zr, Pr, Y, and Mn at a proportion of60:20:10:5:5 (mass ratio). Next, the honeycomb-structured body wasimmersed up to a predetermined height from the outlet end face (exhaustgas outflow side end face), and suction is performed for a predeterminedperiod of time with adjusting the suction pressure and the suction flowrate to have predetermined suction pressure and suction flow rate toload a catalyst on the partition walls, followed by drying at 120° C.for two hours and baking at 550° C. for one hour to obtain acatalyst-loaded honeycomb filter of Example 1. The aforementionedexperiments [1] to [3] were performed. The partition wall properties,composite region/layer properties, and the experiment results are shownin Table 1.

TABLE 1 Composite region/layer property Distance Partition wall propertyCom- from Average Com- posite outer- Evaluation result Rib pore Averageposite region most Full load Pressure Trapping thick- Cell Poros- diam-Particle region depth contour pressure loss with effi- Isostatic nesspitch ity eter diameter depth rate line loss soot ciency strength No.[μm] [mm] [%] [μm] [μm] [μm] [%] [μm] [kPa] [kPa] [%] [MPa] Comp. Ex. 1300 1.47 41 14 3 0 0 50 34 19 85 — Comp. Ex. 2 300 1.47 41 14 3 0 0 2024 18 72 — Comp. Ex. 3 300 1.47 41 14 — 0 0 0 17 17 65 — Example 1 3001.47 41 14 3 10 3.3 20 14 8 87 — Example 2 300 1.47 41 14 3 20 6.7 20 148 89 — Example 3 300 1.47 41 14 3 50 16.7 20 14 8 91 — Example 4 3001.47 41 14 3 80 26.7 20 14 8 91 — Example 5 300 1.47 41 14 3 90 30.0 2014 9 92 — Example 6 300 1.47 41 14 3 100 33.3 20 16 17 92 — Comp. Ex. 4300 1.47 41 14 0.5 20 6.7 20 25 18 91 — Comp. Ex. 5 300 1.47 41 14 0.820 6.7 20 23 17 91 — Example 7 300 1.47 41 14 1 20 6.7 20 15 8 90 —Example 8 300 1.47 41 14 5 20 6.7 20 14 8 91 — Example 9 300 1.47 41 1415 20 6.7 20 14 8 91 — Comp. Ex. 6 300 1.47 41 14 18 20 6.7 20 14 8 73 —Comp. Ex. 7 300 1.47 41 14 3 20 6.7 82 26 16 90 — Example 10 300 1.47 4114 3 20 6.7 80 16 8 90 — Example 11 300 1.47 41 14 3 20 6.7 70 15 8 89 —Example 12 300 1.47 41 14 3 20 6.7 50 16 8 89 — Example 13 300 1.47 4114 3 20 6.7 30 14 9 90 — Example 14 300 1.47 41 14 3 20 6.7 10 14 9 90 —Example 15 300 1.47 41 14 3 20 6.7 5 15 9 91 —

Example 2 to 6

There was obtained a honeycomb-structured body (composite region-formedbody) provided with the same partition wall properties as in Example 1and different from Example 1 in that the composite region depth(thickness of the composite region in the partition wall thickness) was20 μm and that the composite region depth rate (rate of the compositeregion depth with respect to the partition wall thickness) was 6.7%.Further, through the same catalyst-treating step as in Example 1,grinding was performed to have a circular columnar shape. Then, theperipheral face was coated with an outer periphery coat layer of amaterial equivalent to the honeycomb formed body, followed by drying forhardening to obtain a circular columnar honeycomb filter having adiameter of 144 mm, a length of 152 mm, and a cell density of 46.5cells/cm². The honeycomb filter obtained above was employed as Example2. Incidentally, since Examples 3 to 24 employ a circular columnarhoneycomb filter having a diameter of 144 mm, a length of 152 mm, and acell density of 46.5 cells/cm², the description will be omitted. In thesame manner, in Example 3, the honeycomb-structured body (compositeregion-formed body) was obtained in the same manner as in Example 1except that the composite region depth (thickness of the compositeregion in the direction of partition wall thickness) was 50 μm and thatthe composite region depth rate (composite region depth rate withrespect to the thickness of the partition wall) was 16.7% as thecomposite region/layer properties. Further, a honeycomb filter wasobtained through the same steps as in Example 1. The honeycomb filterwas employed as Example 3. In the same manner, in Example 4, thehoneycomb-structured body (composite region-formed body) was obtained inthe same manner as in Example 1 except that the composite region depth(thickness of the composite region in the direction of partition wallthickness) was 80 μm and that the composite region depth rate (compositeregion depth rate with respect to the thickness of the partition wall)was 26.7% as the composite region/layer properties. Further, a honeycombfilter was obtained through the same steps as in Example 1. Thehoneycomb filter was employed as Example 4. In the same manner, inExample 5, the honeycomb-structured body (composite region-formed body)was obtained in the same manner as in Example 1 except that thecomposite region depth (thickness of the composite region in thedirection of partition wall thickness) was 90 μm and that the compositeregion depth rate (composite region depth rate with respect to thethickness of the partition wall) was 30.0% as the composite region/layerproperties. Further, a honeycomb filter was obtained through the samesteps as in Example 1. The honeycomb filter was employed as FIG. 5. Inthe same manner, in Example 6, the honeycomb-structured body (compositeregion-formed body) was obtained in the same manner as in Example 1except that the composite region depth (thickness of the compositeregion in the direction of partition wall thickness) was 100 μm and thatthe composite region depth rate (composite region depth rate withrespect to the thickness of the partition wall) was 33.3% as thecomposite region/layer properties. Further, a honeycomb filter wasobtained through the same steps as in Example 1. The honeycomb filterwas used as Example 6. The thus obtained honeycomb filters with acatalyst of Examples 2 to 6 were subjected to the aforementionedexperiments [1] to [3]. The results of the experiments, partition wallproperties, and composite region/layer properties are shown in Table 1.

Examples 7 to 9

In addition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the average particlediameter was 1 μm as a composite region/layer property was obtained, ahoneycomb filter was obtained through the same steps as in Example 1.The honeycomb filter was employed as Example 7. In addition, after ahoneycomb-structured body (composite region-formed bodies) which was thesame as Example 2 except that the average particle diameter was 1 μm asa composite region/layer property was obtained, a honeycomb filter wasobtained through the same steps as in Example 1. The honeycomb filterwas employed as Example 8. In addition, honeycomb-structured body(composite region-formed body) which was the same as Example 2 exceptthat the average particle diameter was 15 μm as a composite region/layerproperty was obtained, a honeycomb filter was obtained through the samesteps as in Example 1. The honeycomb filter was employed as Example 9.The thus obtained honeycomb filters with a catalyst of Examples 7 to 9were subjected to the aforementioned experiments [1] to [3]. The resultsof the experiments, partition wall properties, and compositeregion/layer properties are shown in Table 1.

Examples 10 to 15

In addition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the distance from theoutermost contour line was 80 μm as a composite region/layer propertywas obtained, a honeycomb filter was obtained through the same steps asin Example 1. The honeycomb filter was employed as Example 10. Inaddition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the distance from theoutermost contour line was 70 μm as a composite region/layer propertywas obtained, a honeycomb filter was obtained through the same steps asin Example 1. The honeycomb filter was employed as Example 11. Inaddition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the distance from theoutermost contour line was 50 μm as a composite region/layer propertywas obtained, a honeycomb filter was obtained through the same steps asin Example 1. The honeycomb filter was employed as Example 12. Inaddition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the distance from theoutermost contour line was 30 μm as a composite region/layer propertywas obtained, a honeycomb filter was obtained through the same steps asin Example 1. The honeycomb filter was employed as Example 13. Inaddition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the distance from theoutermost contour line was 10 μm as a composite region/layer propertywas obtained, a honeycomb filter was obtained through the same steps asin Example 1. The honeycomb filter was employed as Example 14. Inaddition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the distance from theoutermost contour line was 5 μm as a composite region/layer property wasobtained, a honeycomb filter was obtained through the same steps as inExample 1. The honeycomb filter was employed as Example 15. The thusobtained catalyst-loaded honeycomb filters of Examples 10 to 15 weresubjected to the aforementioned experiments [1] to [3]. The results ofthe experiments, partition wall properties, and composite region/layerproperties are shown in Table 1.

Examples 16 to 19

In addition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the porosity was 35%as a partition wall property was obtained with adjusting the particlediameter size and distribution (sharp, broad, two peak distribution,etc.) of the raw material to be used and the pore former (particlediameter, particle diameter distribution, and addition amount), ahoneycomb filter was obtained through the same steps as in Example 1.The honeycomb filter was employed as Example 16. In the same manner,after a honeycomb-structured body (composite region-formed body) whichwas the same as Example 2 except that the porosity was 50% as apartition wall property was obtained, a honeycomb filter was obtainedthrough the same steps as in Example 1. The honeycomb filter wasemployed as Example 17. In the same manner, after a honeycomb-structuredbody (composite region-formed body) which was the same as Example 2except that the porosity was 60% as a partition wall property wasobtained, a honeycomb filter was obtained through the same steps as inExample 1. The honeycomb filter was employed as Example 18. In the samemanner, after a honeycomb-structured body (composite region-formed body)which was the same as Example 2 except that the porosity was 75% as apartition wall property was obtained, a honeycomb filter was obtainedthrough the same steps as in Example 1. The honeycomb filter wasemployed as Example 19. The thus obtained catalyst-loaded honeycombfilters of Examples 16 to 19 were subjected to the aforementionedexperiments [1] to [4]. The results of the experiments, partition wallproperties, and composite region/layer properties are shown in Table 2.

Examples 20 to 24

In addition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the average porediameter was 5 μm as a partition wall property was obtained, a honeycombfilter was obtained through the same steps as in Example 1. Thehoneycomb filter was employed as Example 20. In addition, after ahoneycomb-structured body (composite region-formed body) which was thesame as Example 2 except that the average pore diameter was 10 μm as apartition wall property was obtained, a honeycomb filter was obtainedthrough the same steps as in Example 1. The honeycomb filter wasemployed as Example 21. In addition, after a honeycomb-structured body(composite region-formed body) which was the same as Example 2 exceptthat the average pore diameter was 30 μm as a partition wall propertywas obtained, a honeycomb filter was obtained through the same steps asin Example 1. The honeycomb filter was employed as Example 22. Inaddition, after a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except that the average porediameter was 35 μm as a partition wall property was obtained, ahoneycomb filter was obtained through the same steps as in Example 1.The honeycomb filter was employed as Example 23. In addition, after ahoneycomb-structured body (composite region-formed body) which was thesame as Example 2 except that the average pore diameter was 40 μm as apartition wall property was obtained, a honeycomb filter was obtainedthrough the same steps as in Example 1. The honeycomb filter wasemployed as Example 24. The thus obtained catalyst-loaded honeycombfilters with a catalyst of Examples 20 to 24 were subjected to theaforementioned experiments [1] to [3]. The results of the experiments,partition wall properties, and composite region/layer properties areshown in Table 2.

TABLE 2 Composite region/layer property Distance Partition wall propertyCom- from Average Com- posite outer- Evaluation result Rib pore Averageposite region most Full load Pressure Trapping thick- Cell Poros- diam-Particle region depth contour pressure loss with effi- Isostatic nesspitch ity eter diameter depth rate line loss soot ciency strength No.[μm] [mm] [%] [μm] [μm] [μm] [%] [μm] [kPa] [kPa] [%] [MPa] Comp. Ex. 8300 1.47 33 14 3 20 6.7 20 36 17 91 3.5 Example 16 300 1.47 35 14 3 206.7 20 16 9 90 3.3 Example 17 300 1.47 50 14 3 20 6.7 20 14 8 91 2.7Example 18 300 1.47 60 14 3 20 6.7 20 14 8 91 2.2 Example 19 300 1.47 7514 3 20 6.7 20 14 8 90 1.1 Comp. Ex. 9 300 1.47 78 14 3 20 6.7 20 14 890 0.5 Comp. Ex. 10 300 1.47 41 4 3 20 6.7 20 37 16 91 — Example 20 3001.47 41 5 3 20 6.7 20 19 9 91 — Example 21 300 1.47 41 10 3 20 6.7 20 168 90 — Example 22 300 1.47 41 30 3 20 6.7 20 14 8 91 — Example 23 3001.47 41 35 3 20 6.7 20 14 8 89 — Example 24 300 1.47 41 40 3 20 6.7 2014 8 87 — Comp. Ex. 11 300 1.47 41 43 3 20 6.7 20 15 8 71 —

Comparative Example 1 to 3

After a honeycomb-structured body was obtained in the same manner as inExample 1, in a state without supplying particles in the compositeregion, the peripheral face of the honeycomb-structured body was coatedwith the outer periphery coat layer formed of a material equivalent tothe honeycomb formed body, followed by drying for hardening to obtain acircular columnar honeycomb filter having a diameter of 144 mm, a lengthof 152 mm, a partition wall thickness of 300 μm, and a cell density of46.5 cells/cm². Incidentally, since Comparative Examples 2 to 11 employa circular columnar honeycomb filter having a diameter of 144 mm, alength of 152 mm, a partition wall thickness of 300 μm, and a celldensity of 46.5 cells/cm², the description will be omitted. Further, inthe same manner as in Example 1, catalyst coating was performed toobtain a catalyst-loaded honeycomb filter. The catalyst-loaded honeycombfilter had a rib thickness (partition wall thickness) of 300 μm, a cellpitch of 1.47 mm, a porosity of 41%, and an average pore diameter of 14μm as partition wall properties and an average particle diameter of 3μm, a composite region depth (thickness of the composite region in thedirection of partition wall thickness) of 0 μm, a composite region depthrate (the rate of the composite region depth with respect to thepartition wall thickness) of 0%, and a distance from the outermostcontour line of 50 μm as composite region/layer properties, and it wasemployed as Comparative Example 1. In the same manner, a catalyst-loadedhoneycomb filter which was the same as that of Comparative Example 1except that the distance from the outermost contour line was 20 μm wasemployed as Comparative Example 2. In the same manner, a catalyst-loadedhoneycomb filter which was the same as that of Comparative Example 1except that the distance from the outermost contour line was 0 μm with“-” for the “average particle diameter” was employed as ComparativeExample 3. Thus, the Comparative Examples 1 to 3 were subjected to theaforementioned experiments [1] to [3]. The results are shown in Table 1.

Incidentally, in Comparative Examples 1 to 3 shown in Table 1, that the“composite region depth” was “0” in the “composite region/layerproperties” means that there was no particle deposition in the compositeregion on the downstream side of the surface layer reference line andthat particles were deposited only above the surface layer referenceline (on the partition wall surface layer side on the upstream side ofthe surface layer reference line (partition wall surface side on theupstream side of the surface layer reference line)). In the same manner,the “average particle diameter” in the “composite region/layerproperties” of Comparative Examples 1 and 2 shows the particle diameterof the particle assemblages present on the upstream side of the surfacelayer reference line (on the partition wall surface layer side on theupstream side of the surface layer reference line (partition wallsurface side on the upstream side of the surface layer reference line)).Incidentally, the “distance from the outermost contour line” in the“composite region/layer properties” shows the distance from theoutermost contour line to the particle assemblages present on theupstream side of the surface layer reference line (on the partition wallsurface layer side on the upstream side of the surface layer referenceline (partition wall surface side on the upstream side of the surfacelayer reference line)). In addition, that the “average particlediameter” in the “composite region/layer properties” of ComparativeExample 3 is “-” means that both the “composite region depth” and the“distance from the outermost contour line” were zero, i.e., conventionalpartition walls where no particle deposits.

Comparative Example 4 to 7

In the same manner, a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except for the average particlediameter of 0.5 μm as a composite region/layer property was obtained.Further, a honeycomb filter was obtained through the same steps as inExample 1. The honeycomb filter was employed as Comparative Example 4.In the same manner, a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except for the average particlediameter of 0.8 μm as a composite region/layer property was obtained.Further, a honeycomb filter was obtained through the same steps as inExample 1. The honeycomb filter was determined as Comparative Example 5.In the same manner, a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except for the average particlediameter of 18 μm as a composite region/layer property was obtained.Further, a honeycomb filter was obtained through the same steps as inExample 1. The honeycomb filter was employed as Comparative Example 6.In the same manner, a honeycomb-structured body (composite region-formedbody) which was the same as Example 2 except for the distance from theoutermost contour of 82 μm as a composite region/layer property wasobtained. Further, a honeycomb filter was obtained through the samesteps as in Example 1. The honeycomb filter was employed as ComparativeExample 7. Thus, the Comparative Examples 4 to 7 were subjected to theaforementioned experiments [1] to [3]. The results are shown in Table 1.

Comparative Example 8 to 11

In addition, a honeycomb-structured body (composite region-formed body)which was the same as Example 2 except for the porosity of 33% as apartition wall property was obtained with adjusting the particlediameter size and distribution (sharp, broad, two distribution) of theraw material to be used and adjusting the pore former (particlediameter, particle diameter distribution, addition amount). Further, ahoneycomb filter was obtained through the same steps as in Example 1.The honeycomb filter was determined as Comparative Example 8. In thesame manner, a honeycomb-structured body (composite region-formed body)which was the same as Example 2 except that the porosity was 78% as apartition wall property was obtained. Further, a honeycomb filter wasobtained through the same steps as in Example 1. The honeycomb filterwas employed as Comparative Example 9. In the same manner, ahoneycomb-structured body (composite region-formed body) which was thesame as Example 2 except that the average pore diameter was 4 μm as apartition wall property was obtained. Further, a honeycomb filter wasobtained through the same steps as in Example 1. The honeycomb filterwas employed as Comparative Example 10. In the same manner, ahoneycomb-structured body (composite region-formed body) which was thesame as Example 2 except that the average pore diameter was 43 μm as apartition wall property was obtained. Further, a honeycomb filter wasobtained through the same steps as in Example 1. The honeycomb filterwas employed as Comparative Example 11. Thus, Comparative Examples 8 to11 were subjected to the aforementioned experiments [1] to [3]. Further,Comparative Examples 8 and 9 were subjected to the aforementionedexperiment [4]. The results are shown in Table 2.

(Discussion)

As shown in Table 1, good results could be obtained in Examples. On theother hand, in Comparative Example 3, since the composite region was notformed in the partition walls, it was confirmed that pressure loss withsoot is high and that the trapping efficiency is low. In addition, inComparative Examples 1 and 2, since the rate of composite region depthwas 0, a dense layer of only simulated ash particles was formed on thepartition wall surface layer. Therefore, the gas permeability remarkablyfell, and the rate of causing the initial pressure loss and pressureloss with soot rose to a large extent. Incidentally, in Example 6, thecomposite region became too large, and, as a result, the rate ofclogging partition wall pores became high. Therefore, the gaspermeability became small, and the pressure loss incidence rate of thepartition walls rose. However, since it was well balanced in comparisonwith other Comparative Examples, it is included in Examples in thisregard. In addition, in Comparative Examples 4 and 5, diameter of theparticles forming the composite was too small, and the particlesaggregated and were densified. Therefore, the gas permeability fell, andthe pressure loss incidence rate of the partition wall rose. Further, inComparative Example 6, the pressure loss incidence rate of the partitionwalls rose. Further, in Comparative Example 6, since the particlediameter was too large, partition wall open pores could not be cloggedefficiently. Therefore, sufficient trapping efficiency could not beobtained. In addition, in Comparative Example 7, since the distance ofthe deposited particles from the outermost contour is large, the regionwhere the composite-forming particles having small diameters bond toeach other became extremely large. Therefore, the effective volume ofexhaust gas inflow side cells became small, and the line resistance whenexhaust gas passes through the cells rose, and the pressure lossincidence rate of partition walls rose. In Comparative Example 8,porosity was too low, and the pore passages became small. Therefore, thegas permeability fell, and the pressure loss incidence rate of thepartition walls rose. In Comparative Example 9, since the porosity wastoo high, the isostatic strength fell. When it is 1.0 or less, there isa high possibility that a crack is caused upon canning. In addition, inComparative Example 10, since pores were small, the gas permeabilitybecame small, and the pressure loss incidence rate of the partitionwalls rose. In addition, in Comparative Example 11, the pore size wastoo large to sufficiently clog the pores even when the composite regionwas formed. Therefore, the trapping efficiency was not sufficient. Thus,in the Comparative Examples, it was confirmed that a defect was easilycaused and that operability was low.

INDUSTRIAL APPLICABILITY

A honeycomb filter of the present invention can suitably be used fortrapping or cleaning up particulates contained in exhaust gas dischargedfrom an internal combustion engine such as a diesel engine, an ordinaryvehicle engine, and an engine of a large automobile such as a truck anda bus or various combustion apparatuses.

DESCRIPTION OF REFERENCE NUMERAL

1, 1A: honeycomb filter, 3: cell, 4: partition wall, 4 a: surface layerportion (composite region), 5: particles (to be deposited), 7: open pore(pore formed in the surface layer), 11 a: open end portion on one side,11 b: open end portion, 13: plugging portion, 17: outermost contour,114: partition wall, 115: inlet layer, 117: soot, G, G1, G2: exhaustgas, N: neck portion, R1, R2: particle, Z1: exhaust gas inflow side, Z2:mid-flow portion (mid-flow region), Z3: exhaust gas outflow side

1. A honeycomb filter comprising a base material having ahoneycomb-structured substrate provided with a plurality of cellsseparated by partition walls of porous ceramic having pores andfunctioning as exhaust gas passages, wherein plugging portions areformed alternately in one side open end portions and the other side openend portions of the plural cells, at least in pores formed in a surfacelayer of the partition walls and pores in the partition walls, acomposite region is formed by depositing particles having an averageparticle diameter smaller than an average pore diameter of the partitionwalls in a surface layer portion of the partition walls on the exhaustgas inflow side, the partition walls have an average pore diameter of 5to 40 μm and a porosity of 35 to 75%, the particles deposited have anaverage particle diameter of 1 to 15 μm, and the composite region has aheight of 80 μm or less with respect to the partition wall surfacedirection from the outermost contour line of the partition walls.
 2. Thehoneycomb filter according to claim 1, wherein the composite region isformed in the pores formed in the surface layer of the partition wallsand the pores in the partition walls in the range from a surface layerreference line of the partition walls on the exhaust gas inflow side toa position of 30% of the partition wall thickness.
 3. The honeycombfilter according to claim 1, wherein the composite region is formed inthe pores formed in the surface layer of the partition walls and thepores in the partition walls in the range from a surface layer referenceline of the partition wall on the exhaust gas inflow side to a positionof the depth of at most 4 times the average pore diameter of thepartition walls.
 4. The honeycomb filter according to claim 1, whereinthe partition walls have a porous structure constituted of a pore-linkedform and wherein the composite region has a porous structure constitutedof a particle-liked form.
 5. The honeycomb filter according to claim 1,wherein the particles to be deposited in the pores formed in the surfacelayer of the partition walls and the pores in the partition walls areformed of the same material as that for the partition walls.
 6. Thehoneycomb filter according to claim 1, wherein the partition walls areof cordierite or aluminum titanate.
 7. The honeycomb filter according toclaim 1, wherein the particles to be deposited in the pores formed inthe surface layer of the partition walls and the pores in the partitionwalls are connected to one another by sintering of the particles.
 8. Thehoneycomb filter according to claim 1, wherein a catalyst is loaded on apart of or the entire portion of the partition walls and/or a part of orthe entire portion of the composite region.
 9. A method for producing ahoneycomb filter, the method comprising: forming a honeycomb formed bodyby subjecting a forming raw material containing a ceramic raw materialto extrusion forming and forming plugging portions alternately in oneside open end portions and the other side open end portions of theplural cells of the honeycomb formed body, firing the honeycomb formedbody to form a honeycomb fired body, supplying particles having anaverage particle diameter smaller than the average pore diameter of thepartition walls from the one side open end portions of the honeycombfired body by a solid-gas two-phase flow, and at least in pores formedin the surface layer of the partition walls and the pores in thepartition walls, forming a composite region by depositing particleshaving an average particle diameter smaller than the average porediameter of the partition walls in a surface layer portion of thepartition walls on the exhaust gas inflow side; wherein the partitionwalls have an average pore diameter of 5 to 40 μm and a porosity of 35to 75%, the particles deposited have an average particle diameter of 1to 15 μm, and the composite region has a height of 80 μm or less withrespect to the partition wall surface direction from the outermostcontour line of the partition walls.
 10. A method for producing ahoneycomb filter, the method comprising: forming a honeycomb formed bodyby subjecting a foaming raw material containing a ceramic raw materialto extrusion forming and forming plugging portions alternately in oneside open end portions and the other side open end portions of theplural cells of the honeycomb formed body, firing the honeycomb formedbody to form a honeycomb fired body, supplying particles having anaverage particle diameter smaller than the average pore diameter of thepartition walls from the one side open end portions of the honeycombfired body by a solid-gas two-phase flow, at least in pores formed inthe surface layer of the partition walls and pores in the partitionwalls, forming a composite region by depositing particles having anaverage particle diameter smaller than the average pore diameter of thepartition walls in a surface layer portion of the partition walls on theexhaust gas inflow side, and further performing a thermal treatment;wherein the partition walls have an average pore diameter of 5 to 40 μmand a porosity of 35 to 75%, the particles deposited have an averageparticle diameter of 1 to 15 μm, and the composite region has a heightof 80 μm or less with respect to the partition wall surface directionfrom the outermost contour line of the partition walls.
 11. A method forproducing a honeycomb filter, the method comprising: forming a honeycombformed body by subjecting a forming raw material containing a ceramicraw material to extrusion forming and forming plugging portionsalternately in one side open end portions and the other side open endportions of the plural cells of the honeycomb formed body, firing thehoneycomb formed body to form a honeycomb fired body, loading a catalyston the partition walls of the honeycomb fired body to obtain acatalyst-loaded honeycomb-structured body, supplying particles having anaverage particle diameter smaller than the average pore diameter of thepartition walls from the one side open end portions of thecatalyst-loaded honeycomb-structured body by a solid-gas two-phase flow,at least in pores formed in the surface layer of the partition walls andpores in the partition walls, forming a composite region by depositingparticles having an average particle diameter smaller than the averagepore diameter of the partition walls in a surface layer portion of thepartition walls on the exhaust gas inflow side, and further performing athermal treatment; wherein the partition walls have an average porediameter of 5 to 40 μm and a porosity of 35 to 75%, the particlesdeposited have an average particle diameter of 1 to 15 μm, and thecomposite region has a height of 80 μm or less with respect to thepartition wall surface direction from the outermost contour line of thepartition walls.
 12. The method for producing a honeycomb filteraccording to claim 9, wherein the method comprises: supplying particleshaving an average particle diameter smaller than the average porediameter of the partition walls from one side open end portion of thehoneycomb fired body, and simultaneously, sucking the particles from theother open end portions of the honeycomb fired body to deposit theparticles in the pores formed in the partition walls on the exhaust gasinflow side to form a composite region.
 13. The honeycomb filteraccording to claim 2, wherein the composite region is formed in thepores formed in the surface layer of the partition walls and the poresin the partition walls in the range from a surface layer reference lineof the partition wall on the exhaust gas inflow side to a position ofthe depth of at most 4 times the average pore diameter of the partitionwalls.
 14. The honeycomb filter according to claim 13, wherein thepartition walls have a porous structure constituted of a pore-linkedfoam and wherein the composite region has a porous structure constitutedof a particle-liked form.
 15. The honeycomb filter according to claim14, wherein the particles to be deposited in the pores formed in thesurface layer of the partition walls and the pores in the partitionwalls are formed of the same material as that for the partition walls.16. The honeycomb filter according to claim 15, wherein the partitionwalls are of cordierite or aluminum titanate.
 17. The honeycomb filteraccording to claim 16, wherein the particles to be deposited in thepores formed in the surface layer of the partition walls and the poresin the partition walls are connected to one another by sintering of theparticles.
 18. The honeycomb filter according to claim 17, wherein acatalyst is loaded on a part of or the entire portion of the partitionwalls and/or a part of or the entire portion of the composite region.19. The method for producing a honeycomb filter according to claim 10,wherein the method comprises: supplying particles having an averageparticle diameter smaller than the average pore diameter of thepartition walls from one side open end portion of the honeycomb firedbody, and simultaneously, sucking the particles from the other open endportions of the honeycomb fired body to deposit the particles in thepores formed in the partition walls on the exhaust gas inflow side toform a composite region.
 20. The method for producing a honeycomb filteraccording to claim 11, wherein the method comprises: supplying particleshaving an average particle diameter smaller than the average porediameter of the partition walls from one side open end portion of thehoneycomb fired body, and simultaneously, sucking the particles from theother open end portions of the honeycomb fired body to deposit theparticles in the pores formed in the partition walls on the exhaust gasinflow side to form a composite region.